What are the primary colours of light?

This Q&A is about light colours. Paint colours are substances, and different from light colours.

If you hold up a glass prism to a beam of sunlight, you'll see the light form a rainbow of colours. This is called the spectrum. It consists of all the colours that make up "white" light.

Although you might be able to see seven colours in the spectrum, the white light is really made up of three basic colours. These are called the primary colours because they cannot be made from any other colours. The primary colours of light are red-orange, green, and violet blue. The other colours you see in spectrums or rainbows are made by a mixture of the primary colours.

When the naked eye looks at the spectrum, it can see three mixed colours, which are called secondary colours. The secondary colours in light are green-blue, yellow, and magenta-red. You can produce these colours by mixing the primary colours in certain combinations.