Colour is a powerful thing, and it often lies at the heart of our perception of the world. Colours help us identify specific objects and associate properties to them. Colours also help us interpret emotions and recognise real world threats. However, an interesting question is where did this sense of colour come from?
How we see in colour
It all starts with your eyes. Unlike many other living animals, human eyes are designed to interpret a wide range of light wavelengths which helps us identify colours. On a technical level, colours are simply different spectrums of wavelengths either travelling faster or slower towards our eyes and into our brain. We are good at it, but before you get big headed, we aren't the best at interpreting colours: Many animals have a colour perception ability that is far beyond our comprehension, for example, the Mantis Shrimp: Believe it or not the mantis shrimp has 4 times better colour vision than humans do.
However, seeing a colour is one thing, interpreting it is something else. So how did we come to associate different colours with different emotions, and physical reactions, even physical danger triggers? That is a completely different science altogether. Naturally, we (and many other animals in the kingdom) associate brighter colours like red and yellow to danger signs. Colour in this sense has the power to alert us to dangers before we are fully aware of them.
It all boils down to the fact that many brightly-coloured animals, bugs and insects tend to be either poisonous or toxic, and we have learnt, probably through a few nasty accidents, that they should be avoided. The same thing, all designed by mother nature, applies to plant life too: Mushrooms for example tend to be dangerous if they are brightly coloured, and berries. This, combined with millions of years of social adaptation, means we have developed the instinct to avoid brightly coloured objects, and we have applied this principle to the things we create. For example: traffic lights, have you ever wondered why traffic lights go specifically in the order red, amber, green?
Have you ever wondered why stop signs and many signs for danger are red? Why not green? It's simple, even though it is only an extra precaution in most cases, a red sign naturally conveys the word stop, or a sense of danger better than a green one. It's simply more eye-catching.
Colour and emotion in humans
We associate many colours with specific emotions or human traits, which can vary across cultures. Here in the west you might hear of someone having the blues: Having “the blues” means feeling sad and lonely. The colour has even been applied to a genre of music; the blues. Maybe you have seen red (felt very angry), and yet the colour red is often associated with love, as well as danger, which might make sense in a strange kind of way. Being given a red rose is often an expression of romance, and red hearts cover every surface around Valentine's Day. Have you ever been green with envy? Yellow is associated with cowardice, and white with purity. In history, black and white are historically associated with good and evil, the colour black abounds over Halloween, but it is also the colour of mourning. As you can see colours have been given meaning by our society, and we often assign them roles based on our own experience. You must have a favourite colour.
The fact is colours hold a great importance in our perception of the outside world. Our ability to see in colour helps us navigate the obstacles around us better, and they play a major role in threat/danger detection. If you have difficulty perceiving certain colours (we call it being colour blind) several careers are closed to you.
Though not so important in adults, for children the basic ability to separate danger from safety using colour, plays an important role in keeping safe! Which is why colour is extremely beneficial as a method of communication within human society.
Search Google for "colour theory", "colour therapy" and "colour psychology".