Posted in Psychology & Medicine


What colour do you associate with the letter “E”? What sound do you hear when you feel the fluffiness of cotton? These sound strange to most people as we experience the senses in distinct ways. However, for 4% of the population, this is a completely normal experience.

Synaesthesia (“joined sensation”) is the neurological phenomenon where two or more senses are coupled together. This creates two kinds of synaesthesia: projection, where you physically sense something (such as seeing a purple circle when hearing piano music), and association, where you associate the sense with another sense (“that sounds quite orange”).

The most common form of synaesthesia that is reported is grapheme-colour synaesthesia, where certain people perceive letters and numbers as different colours. However, there are various kinds of synaesthesia, such as chromesthesia, where people associate sounds with colours (previously called “coloured hearing”). In fact, almost every combination of senses have been described, with some individuals experiencing multiple senses at the same time.


The exact origin and mechanism of synaesthesia are yet to be fully explained. The most likely explanation is that in the brain of synaesthetes, the neural pathways for the various senses cross-over more than they should, causing the simultaneous activation. There are already some cross-overs between these pathways, as evidenced by various sensory illusions that the average person can enjoy. For example, a ventriloquist can fool the audience into thinking the puppet is talking as we hear speech and see the puppet’s mouth moving.

An alternative explanation is that there may be an element of ideasthesia – where concepts are paired with sensory experience. This would mean that synaesthetes are experiencing sensations due to the idea something represents, not because of the original sensory stimulus.

For example, when a synaesthete describes that the word “tree” tastes like brie cheese, it might not be the sound of the word, but rather the concept of a tree that triggers the sensation. We actually see examples of this in day to day life in the form of metaphors. We describe a wine having a round taste or a person being sweet.

There is much to learn about the phenomenon, but synaesthesia has already deepened our understanding of how we perceive the world, process it and commit it to memory through the use of associations and mnemonics.

Posted in Philosophy

Mary And The Black And White Room

Mary is a brilliant scientist who specialises in colour. She knows everything about colour – the spectrum, wavelengths, properties of light, the mechanism of how human vision works… She knows exactly how a certain wavelength of light will excite the retina and what kind of electrical impulse it will send in the brain. However, Mary has never seen colour. She has lived all of her life in a black and white room and can only observe the world through a black and white TV screen. The question is: if Mary was to leave the room and see the colourful world for what it is, would she learn something new?

Considering that Mary already knows everything theoretical about colour, would her seeing colour change anything? Or is the experience of seeing a colour something that you cannot learn without actually experiencing it?

This was a thought experiment proposed by Frank Jackson to question the nature of knowledge. Is physical knowledge truly everything, or is there something more than that? In philosophy, there is a concept called qualia, which describes the subjective, qualitative properties of experiences. That is, experience is a unique type of knowledge that cannot be learnt without experiencing it first-hand.

A further expansion of this idea is the refutation of physicalism – the school of thought that argues that everything (including knowledge and the mind) is physical. The logic is that since Mary knew everything “physical” about colour before leaving the room, her learning “something’ (i.e. experience of colour) is a direct argument against all knowledge being physical, as she learnt something “new”.

Another way to look at it is this. Some things in life can only be learnt through experiencing it. It is not enough trying to learn about life and the world purely from stories and books. To truly learn everything, you must get out there and experience it yourself.

Posted in History & Literature

Evolution Of Colour

We often take the beauty of colour for granted. How would you explain the colour red to a blind person? With that in mind, how do we know that the colour we see with our own eyes is the same hue that others see? A scholar by the name of William Gladstone came across a similar question in 1858 while studying ancient Greek literature. He noticed that in most literature of ancient times, the description of colour was wildly inconsistent, such as the sea being described as “wine-dark”, the sky being “copper-coloured” and other oddities such as violet sheep and green honey. After further analysis, Gladstone found that white and black were referenced frequently, while other colours were much rarer, with red, yellow and green being the most common colours respectively.

Another scholar named Lazarus Geiger expanded on Gladstone’s research and found that throughout ancient literature – including the Bible, Hindu poems, ancient Chinese stories and Norse tales – described beautiful scenes while omitting a certain detail: a blue sky. It appeared that the colour “blue” did not appear in most languages until a certain point in time, despite the people having lived under the same blue sky that we do now.

Geiger tracked the appearance of different colours in different languages and found a pattern of development. Each language would typically describe white (light) and black (dark) first. The next colour to develop was red, then yellow and green, with blue being one of the last colours to appear. This is likely related to the abundance of each colour (e.g. blood, dirt, vegetation) and the ease of making coloured dye (blue dye is notoriously difficult to make).

This raises an interesting question: if the ancient Greeks did not have a word for the colour blue, could they still perceive the colour blue? Biologically speaking, our eyes are not so different to that of the ancient Greeks. But of course vision is a two-part processyour eye captures the image and then your brain processes the image. Does language have a significant enough impact on how we perceive our world?


There is a tribe in Namibia whose language does not distinguish blue and green. A study was held where people from this tribe were shown a circle of 12 squares – 11 green and 1 blue. To the researcher’s intrigue, the men and women of the Himba tribe could not tell which square was the odd one out – suggesting that their brain was processing the two colours as identical. However, the Himba language has more words distinguishing shades of green than English. In another study involving a circle of green squares with one square being a slightly different shade of green, the Himba tribe could pick out the different square much more easily than English-speakers.

The so-called “colour debate” is a hotly debated topic, with some arguing that language plays a crucial role in determining our perception of the world, while others state that language is separate to our senses. What did the ancient Greeks see when they gazed up into the sky? If we cannot describe something with words, then does it truly exist? But one thing is clear – things are not always as they seem.

Posted in Science & Nature


Why is the sky blue? This is because of a phenomenon called Rayleigh scattering where molecules and tiny particles in the atmosphere scatter direct sunlight. Light scatters at different amounts depending on its frequency. Because of this, blue and violet light (short-wavelength light) scatters more than the other colours, causing the sky to be blue. But during sunrise and sunset, the light enters the atmosphere from an angle, causing blue and green light to be so scattered that you cannot see it. This produces a red or orange colour.

The deep ocean is blue for a similar reason; red and yellow light is absorbed while blue becomes scattered by the water. However, the colour of the sea is also largely dependent on the colour of the sky at the time, as it reflects the sky. The colour of the sea may change due to algae in the water, which can make it green, brown or even red.

A similar form of light scattering called the Tyndall effect is responsible for blue eyes, caused by a turbid layer in the iris. The Tyndall effect can also be seen in a glass of water mixed with milk, or flour suspended in water.

Blue has one of the most interesting histories compared out of all the colours. In the ancient world, blue was considered a lowly colour, with some cultures such as the ancient Greeks not even considering it a “real colour” such as red, black, white and yellow. In fact, the Greeks did not have a word for the colour blue; it was merely called bronze colour. The ancient Romans considered blue the colour of barbarians. The Romans stereotyped blue-eyed women as promiscuous and blue-eyed men as aggressive and foolish. Only the ancient Egyptians liked the colour blue, as they considered it a colour of divinity. They made blue dye from copper.

Perhaps the hatred for the colour blue was due to the difficulty of making blue dyes. This all changed nearer to medieval times as artists and dyers successfully created blue dyes from minerals such as lapis lazuli, azurite and cobalt. Blue became the colour of the Virgin Mary. Artists began painting the sky and the sea as blue, which were previously depicted using black, white and green. Nobles began wearing blue instead of the traditional red and purple, and dyers followed this trend by devising better blue dyes with a variety of shades.


This led to the thriving of blue dye industries in European cities such as Amiens, Toulouse and Erfurt, where blue dye was made from a plant called woad. Although this was a very lucrative business, blue was still a very expensive and difficult colour to use, with the dying process involving soaking the woad in human urine (which contains ammonia) to extract the colour.

Blue became a much more accessible colour in the 18th century when flourishing trade brought indigo from the Americas. Indigo was much easier to use, more concentrated and produced a richer, more stable blue than woad. As blue became more and more popular, synthetic blue dyes were discovered – one of the most famous being Prussian blue which was discovered in Berlin in 1709.

Throughout its history, perhaps the product that best promoted the status of blue as a colour is the denim jean (dyed with indigo blue), invented by Levi Strauss in 1873. 

In modern times, blue is an extremely popular colour that is widely used in art, fashion, architecture etcetera. However, the one field that blue has not yet been able to set foot in is food. Researches show that the colour blue drastically decreases a person’s appetite as it is associated with poison in the natural world.

Posted in Psychology & Medicine


Despite the implied disgusting nature (especially smell) of urine, it is one of the most important types of “samples” used in medicine for diagnostic purposes. Like blood, urine can tell a lot about a person’s health and whether they have a certain disease or not.

One of the earliest recorded uses of urine as a medical test was for the detection of diabetes mellitus. People noticed that the urine of a diabetic would often smell quite sweet, and also taste sweet (it is uncertain how they came to test urine this way). This is because a diabetic has too much glucose (sugar) in their blood, causing it to spill over into the urine as the kidneys become saturated. In fact, the words diabetes mellitus stand for “passing through” (referring to the symptom of frequent urination) and “honey-sweet”. A completely unrelated disease called diabetes insipidus also causes frequent urination, but the urine does not taste sweet, hence “insipidus” (tasteless). This type of etymology is also seen in countries like Korea, China and Japan, where the word 당뇨(糖尿) literally stands for “sugar urine”. Although we no longer taste urine, it is still used to gauge the severity of diabetes by measuring the amount of protein in the urine (due to kidney damage).

There are many other tests one can do with urine to check for certain diseases. The chemical composition of urine tells us about the hydration status of a person, while giving away clues to diseases that cause electrolyte imbalance. It also gives some indication of how well the kidneys can do their job of concentrating urine. Certain markers such as white blood cells and bacteria in the urine can indicate a urinary tract infection. Antibodies in the urine can point towards a certain type of bacteria as the cause of a patient’s pneumonia, or whether a woman is pregnant (βhCG). Looking for proteins or sediments in the urine can be diagnostic of certain kidney diseases such as glomerulonephritis. Even rare diseases such as phaeochromocytomas can be diagnosed from the level of catecholamines in the urine (this is slightly too complex for our scopes).

A more interesting part of urinalysis is looking at the colour of the urine. Urine is usually a yellow colour, ranging in darkness depending on the concentration of urine. But when there are other things in the urine, the colour changes. Reddish urine suggests blood (which is not an indicator of kidney failure as TV shows say), which can be caused by trauma, UTIs, kidney stones or some other disease. Brown urine could be due to muscle breakdown somewhere in the body. Urine can appear very dark if the person has an illness called obstructive jaundice. Eating beetroots can cause your urine to turn bright red, while medications can change your urine colour from anywhere from red to orange to green. Murky or cloudy urine (with an offensive smell) may suggest a UTI.

Perhaps the most interesting urine colour known in medicine is purple. This unique colour is produced in a rare genetic disease called acute intermittent porphyria. If urine is collected from a patient suffering an attack of AIP (causes crippling abdominal pain) then left in the sun or under a UV light, it will turn purple due to certain proteins. Because of this, urine collected to test for AIP is wrapped in tinfoil before sending to the lab (where the chemicals are measured) to limit light exposure.

(Also read the article on how different colours of skin can be of diagnostic importance:

Posted in Psychology & Medicine


They say that human imagination is infinite and limitless. But consider this: can you imagine a colour outside of the visible spectrum? Most likely, you are incapable of thinking of a new colour that cannot be mapped on a standard colour chart. Interestingly, a small proportion of people can see and understand colours beyond the range that the majority of us can see.

The physiology of vision is rather complex, but essentially boils down to the retina (inside lining of the eyeball) acting as a film for the image that you see. Cells known as photoreceptors convert the visual image into electrical signals that are transmitted to the occipital lobe of the brain via the optic nerve. There are two types of photoreceptors: rod cells, which sense movement, and cone cells, which sense colour and provide sharp images (visual acuity). Human beings typically see colour by combining three primary colours: red, green and blue (known as the RGB system). There are cone cells for each primary colour. The brain processes the signals sent by each cone cells and figures out what “colour” you are seeing. Therefore, you can only perceive colours made from a combination of red, green and blue. It is easy to visualise this by playing with colour palettes on computer programs such as Photoshop.

In recent years, it has been speculated that a certain percentage of women have an extra type of cone cell that senses a different wavelength of light. Ergo, they can theoretically sense a greater range of colours compared to someone who has three types of cone cells. This condition is called tetrachromacy (“four colours”). Tetrachromacy is the opposite to colour blindness, which is caused by a deficiency or fault in one or two types of cone cells. To these people, the average person (a trichromat) will appear “colour blind”.

According to one estimate, as many as 12% of women are tetrachromats. Although there are many theoretical barriers to true tetrachromacy, there have been several documented cases of women who perceive colour in much more depth.

The ability to see an extra primary colour is more significant than just a 25% increase in the person’s colour range. An average person can see about 1 million different hues (shades of colours), while a true tetrachromat can see 100 million hues – a hundred-fold increase in the range of colours they can see. One can only wonder what kind of amazing sights a tetrachromat sees when she gazes upon a field of flowers or even a rainbow. Unfortunately, even if a tetrachromat tried to explain the colours she saw to us, we would not be able to grasp the colours as our minds would be incapable of visualising the colours, much like how describing the colour red to a blind person is impossible.

Posted in Life & Happiness

Yellow Ball

If I was to put a yellow ball in front of you and ask what colour the ball is, you would confidently say “yellow”. As you say, the ball appears yellow, but the answer is technically wrong. Strictly speaking, the ball itself is not yellow – it is merely reflecting the colour yellow. The ball only appears yellow because we see the yellow part of the natural light spectrum bouncing off the ball. We cannot say that the essence of the ball is “yellow”. For example, if you were to look at the ball through a red lens, the yellow light would be filtered and you would see a black ball. A person with a certain kind of colour blindness would say the ball has a bluish hue. A butterfly, which sees the ultraviolet spectrum as well, would see a colour we cannot even name.

Human beings judge objects using the vision. We describe an object as we see it and store that information in our brain to define the object. For this purpose, the fact that a colour blind person or a butterfly sees the ball a different colour is irrelevant to us. All we need to know is that object appears yellow to us. But this is only the case for objects. Let us imagine the ball is a person. If everyone in the world sees you as a yellow ball, would that make you a yellow ball? Of course not. However, people worry too much about how others see them. Although other people’s perception does not change our true nature in the slightest, we even go as far as erasing or abandoning our nature to look good in front of another person. Thus, whether our essence is white, black, red, blue or technicolour, when others see us as yellow, we have a tendency to try desperately to become yellow. 

If the world says you are a yellow ball, act crazy and be a red ball. There is not a single reason you should have to hide your true nature. Have confidence in your essence. There is nothing wrong with that.


Posted in Psychology & Medicine


Scrubs is the uniform that surgeons, anaesthetists, emergency department doctors and nurses wear for the freedom and mobility required in activities such as surgery and CPR. Also, since it is owned and washed by the hospital instead of being privately owned, it is more hygienic and helps prevents infections. A noticeable trait of scrubs (and also surgical gowns) is that almost every hospital uses a shade of blue or green instead of white. Why is this?

The reason being, looking at a surgical scene for a long period of time can cause eye fatigue and afterimages due to the redness of blood and organs. Afterimage is a phenomenon that occurs when the retina becomes insensitive to a strong colour and instead making the complementary colour stand out more. Ergo, a surgeon looking at blood and organs for too long will see afterimages of a blue shade, which may cause accidents to happen as it overlaps on white surfaces or the surgical field. Clothing of blue or green colour neutralises the afterimage and is much easier on the eyes, reducing the fatigue. Lastly, blue-green colours have a calming psychological effect, which helps in a high-tension, stressful environment such as in an operating theatre.

Posted in Psychology & Medicine


Normally, babies are dressed in blue for boys and pink for girls to differentiate their sex. Even in adult societies, the colour pink is associated with women. As some women have a particular fondness for the colour, the stereotype deepens. Why is femininity related to the colour pink?

The easiest explanation is that it is simply a social construct. In other words, as society says “pink is a girl’s colour”, the stereotype is set. Although this may seem like a simple answer, it shows the power of the majority’s opinion and stereotypes. As evidence to this theory, one can consider the following excerpt. It is taken from an American magazine from 1918:

“The generally accepted rule is pink for the boys, and blue for the girls. The reason is that pink, being a more decided and stronger colour, is more suitable for the boy, while blue, which is more delicate and dainty, is prettier for the girl”.

As you can see, in the past the opposite was the social norm where pink was a boy’s colour. This shows that pink and women have no direct links. This norm was flipped around the 1940’s and pink is still the symbol for femininity.

There is also some scientific data attempting to explain the phenomenon. One study proposed that as prehistoric humans had gender roles where the men hunted and the women gathered, women evolved to seek out red berries, which are ripe and delicious. Thus, they still have a soft spot for pink things. Also, as one can see from cheek blush and red lipstick being common make-ups, women like to accentuate a flush on the face. Pink cheeks and red lips signify that they are healthy and ready for reproduction, causing men to find the colour attractive. Pink clothes further enhance this effect to make the woman look more attractive. A similar technique is used by monkeys (especially baboons) where the female’s backside turns pink or red to alert the males that she is ready to mate.

Posted in Science & Nature

Complementary Colours

Red, green, blue, white… There are many colours that we can see and there are even more different combinations of colours possible. It is common knowledge that some colours clash with each other while some synergise very well. A common example of a “good combination” is when you use complementary colours. Complementary colours are two colours that oppose each other on the colour wheel, creating an effect where they brighten each other. This makes it very eye-catching and attracts people’s attention. For example, blue and orange make a bright contrast making them a popular colour choice for movie posters. Red and green, and yellow and purple are also examples of complementary colours. Complementary colours are an important concept in art and design as it helps the product stand out.

Complementary colours have an interesting relationship with our sense of sight. If you stare at a colour for a while then quickly look at a blank, white surface, you will see an afterimage of the complementary colour. A good example is when you have your eyes closed under bright sunshine and upon opening your eyes the world seems a blue hue (the blood vessels in your eyelid make the light appear orange as it reaches your eyes). This is because the retinas try to negate the intense colour by downregulating the nervous signals corresponding to that colour, which makes the complementary colour stand out. Furthermore, the photoreceptors in the retina become fatigued after stimulation, causing a reduction in the signals sent for that colour.

Knowing about complementary colours is very useful when designing a sign or poster that easily attracts people.

(Image source