Defining the term "colour"
What is colour? Why can humans see colours? How are they produced?
Colours are an optical phenomenon. For this optical phenomenon, we need light - without light, we can not see colours.
This is how colours are produced in humans:
Light reaches the retina through the eye. In the retina, there are two kinds of light sensitive cells: Rods and cones.
The rods are bright/dark sensitive, while cones are responsible for perceiving colours. The combination of both types of cells allows us to see a wide variety of colours.
There are 3 subtypes of cones that have a different spectral sensitivity (short, middle and long wave fields). These three types combined make it possible for us to see lots of colours and shades.