Colours
Colour can be made by adding together other colours.
Here we can see:
Red light + Blue light = Magenta light
Blue light + Green light = Cyan light
Green light + Red light = Yellow light
Red + Blue + Green = White light as the whole visible spectrum is present.
Addition of red, green and blue light to give white light is known as additive colour mixing. Subtractive colour mixing, you might guess, is the opposite. This is the mixing of magenta, cyan and yellow pigments to give black.
You might have noticed the yellow, magenta and cyan circles on the back of newspapers and it is those three colours combining to give coloured pictures and black text.
Why we see colour
The human eye contains two types of cell which are involved in the interpretation of colour. These are known as rods and cones, the names deriving from the shape of the cells. Rod cells are responsible for seeing under poor lighting conditions and allow humans to distinguish light and dark but not colours. Rod cells are only active when rhodopsin is present and rhodopsin is bleached and destroyed by light.
It is under these conditions, i.e. good lighting, when the cone cells come into action. Cone cells are sensitive to colour and are sensitive to lightness and darkness.
