Good Lord! I hope you're ready for a bit of science. :) Let us start at elements and their chemical compounds shall we? A lot of substances abosrb white light and other emissions, for example, the energy from the sun. The energy levels of the atoms in the substance determine what emissions are 'absorbed' and which are 'reflected'. (I'll add that white light is a combination of what we know as 'the colours of the rainbow). In the case of colour, the enery 'reflected' coincides with the frequency of visible light, and the chemical composition of the substance determines which frequencies are emitted, 'refelcted', from the light 'absorbed'. Say, copper sulphate solution, which is a mid blue. The energy from the sun (in this case, can be white light), hits the molecules in the solution. The energy taken in, 'absorbed', by the molecules is a higher frequency than what is 'reflected' (I would explain why, but that's even more complicated. Blame atom bonding for that). The energy reflected corresponds to visible blue light and this energy hits the eye as blue light, making the copper sulphate solution look blue. It's used in pigments and dyes too. A compound that emits the frequency of light that corresponds to the colour you want, can be made and used in the making of a product, like paint. :) In short, the chemical compound of a substance 'absorbs' and 'reflects' a different frequency of energy, hence making it appear the colour that we see. That might be a little confusing, but there are a lot of aspects of chemistry in that question, so I explained as simply as I could. I don't pretend I'm an expert on this either. :)