Colour is an illusion

Assuming you are not in the dark, (in the physical sense, as opposed to the mental sense of information being withheld), what can you see? To an extent, it depends on how strong the light is, whether it’s a bright sunny day, or grey and overcast, but the likelihood is, you can see colour around you. Perhaps the luscious red of a strawberry, or the rich yellow of a banana, or it might be something quite plain like the sage green of your lounge carpet. But whatever you are looking at, unless you are literally sitting in the dark, and even if you suffer colour vision deficiency (CVD), you will see colours.
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However, it may surprise you to learn, the strawberry, banana, or Persian rug you can see, does not actually have a colour. It is a message being sent from your eyes to your brain, and that message starts when light hits the item you are seeing.

Depending on the shape and structure of the object, the light will be absorbed, reflect and refract, creating a colour that most people will see. There will be some items that reflect more of a particular wavelength than others e.g. a lemon will reflect mainly yellow light.

To prove this, look at the same object in the dark; even if you hold it right in front of your eyes, you won’t see any colour at all.

Here’s the science

Light is made up of wavelengths, and when they hit an object e.g. a tomato, their behaviour will determine the colour you see.

According to complicated quantum laws, it is the arrangement of electrons in the atoms of the item that will absorb and re-emit photons of certain energies, so tomatoes are red because the pigment atoms in the tomato skin absorbs photons of all energies except those that correspond to red wavelengths of light, which are reflected to your eye.

But that is only half the story.

It is when the reflected light is detected by the millions of colour sensitive cells (cones) in your retina, and the electrical messages sent to your brain where the data is processed, that you are able to see the red tomato.

Cones, but no ice cream

There are three types of cone cells that detect blue, green, and red, and humans, known as trichromats, can ‘see’ around three million colours.

Most mammals have only two cones (dichromats), e.g. dogs, and can detect fewer different colours. Other species, including birds, fish, and bees, have four types of cones (tetrachromats), and can discern around 100 million different colours, that’s because the fourth cone is sensitive to ultraviolet colours invisible to the human eye.

Since the early twentieth century, scientists have been researching the possibility of humans being tetrachromats. The theory being that people who suffer a form of CVD known as anomalous trichromacy, may carry the extra cone, and in 2007, a woman was found to have an extra cone enabling her to see four-dimensional colour.

Known as ‘functional tetrachromats, it is believed around 3% of the world’s population has this ability, but it is pure speculation, because it is impossible for a trichromat to see the world as they do, and there maybe many tetrachromats who are unaware they see the world differently from everyone else.

Here’s a final thought; if colours don’t exist per se, what is the true ‘colour’ of everything?