through the periodic table and focus on the green dot as we invert the colours. Don’t

stop staring there until I say. The light is travelling as a wave to your eye, and the

frequency of these wavelengths determines the perceived colour of everything in this

picture and around you. Humans have trichromatic vision, meaning we have three cone cells in

our retinas, each which are sensative to different wavelengths of light: blue, green or red.

Keep looking at the green dot and your brain will do something pretty neat. Did the image

change back to the original colour? Even though you were staring at a black and white image,

your brain perceived it to be in colour.

This phenomenon is known as ‘after imaging’ - after staring long enough at the brightly

coloured image, your cones slowly become fatigued and the supply of photopigment in the respective

cones becomes exhausted, which ultimately stops sending signals to the brain. In the

case of this illusion, the part of the photo where you see cyan, the green and blue cones

become tired and as a result there is increased activity in the unfatigued red cones. So when

the image switched to black and white we see ‘red’ - cyan’s complementary colour.

Growing up, you likely learned about the primary colours red, yellow and blue - and their respective

complementary colours. But things are more complicated when you consider that the primary

colours in your printer are magenta, yellow and cyan, or that the screen you’re watching

this on uses red, green and blue! These are different colour models, where RGB is ‘additive’

meaning the mixing of different lights of colour create new colours - while the other

two are ‘subtractive’ models and absorb different wavelengths of light.

For example, when you hold a yellow object in real life (don’t use a lemon), it’s

actually absorbing every wavelength except yellow - that yellow light bounces back and

hits your eyes. But, when you look at this yellow object through your screen right now it’s actually

not yellow at all. Because your screen can only use red, green, and blue colours,

if you were to zoom in physically on anything yellow, it would actually be a combination

of red and green - and because the wavelength of yellow is between red and green, our brain

interprets this mix as yellow. (YELLOW SCREEN) So what you’re seeing here is in fact not

yellow at all, but it’s stimulating a mix of your red and green cones, which your brain

interprets as yellow.

While plants come in a range of colours, the predominant colour is green, due to chlorophyll,

the energy absorbing pigment found in plants critical for photosynthesis. So, to effectively

attract pollinators such as bees, insects and birds, flowers have evolved to stand out

against green. It’s why you don’t see many green flowers. And flowering plants have

even evolved a suite of different colours to attract specific pollinators - known as

pollinator syndrome. Bird-pollinated flowers are mostly red, potentially to discourage

visits from bees, as their visual system is different than birds, making it hard from

them to discriminate between red and green.

Similarly, we all have our own favourite colours, but why? One theory suggests that colour preference

is gendered, where given the choice between cyan and red, men prefer cyan colours and

women prefer redder colours. Researchers hypothesize this preference has evolved from our hunter-gatherer

societies where women's visual systems were specialized to see ripe red berries against

green foliage. Another theory suggest that we like hues that we associate with pleasant

things - however, pleasant and unpleasant things are often the same colour - we love blue slurpee

but not blue mold.

Investigating these questions of colour had us thinking about links between science and

art. So in our latest AsapTHOUGHT we asked both artists and scientists about how they

view their world.

Check it out with the link in the description

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