Do colours exist in nature or are they merely figments of minds?

Let’s begin with a few words about colours. Our ability to perceive various colours results from the brain-eye coordination. The eye contains colour-sensitive detectors and the brain processes signals they transmit and thereby generates colour impressions. It is important to be aware of the fact that apart from being perceived through such impressions, colour can also be measured. It is a well-defined physical quantity and there are suitable tools and procedures which allow for instance to unequivocally determine the colour of paint. 

Colours are associated with electromagnetic wavelengths of light. In nature, there is electromagnetic radiation of different wavelengths: from nanometres and even fractions of those (X-rays, gamma radiation) to tens, hundreds and thousands of metres (radio waves). The visible spectrum, which can be registered by the human eye and interpreted by the brain as colours, is the radiation of 400 to 700-nanometre-wavalength. A wavelength of 400 nm is interpreted by our brain as the violet colour, whereas a wavelength of 700 nm is perceived as red. The intermediate wavelengths are responsible for the perception of the remaining primary colours. Our eyes often receive a combination of different wavelengths, which we interpret as yet another colour (being a  mixture of so-called primary colours), therefore we hardly ever come across monochromatic light of a single wavelength.

Light, and thereby electromagnetic waves, reaches the eyes directly from its source through the pupils to the fundus of the eye. The eye contains receptors sensitive to light, i.e. to the force and length of electromagnetic waves, which are known as rods and cones. Rods are responsible for the perception of shapes and do not distinguish particular colours, and they are most sensitive to wavelengths of approximately 500 nm. Contrary to the rods, the cones are all individually connected with the brain, which influences significantly the quality and acuity of vision. It is the cones which are responsible for the perception of colours in the eye. They process signals coming from the light and transmit them further to the brain, where colour impressions are generated. Thanks to the receptors located in the eye, we are able to see the colourful side of the world, regardless of whether we are short-sighted, long-sighted, astigmatic or have perfectly healthy eyes.

All in all, we can by all means say that colours exist in nature — as they would even if no humans or other creatures with eyes existed, for it would not change the fact that electromagnetic waves of lengths corresponding to the visible spectrum do exist and had already existed before life appeared on Earth.

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