How we see colour
To understand how this works we need to think about how we see. We see objects because light is being reflected off of the object and into our eyes. Most of the light we encounter is white light, white light is made of all the colours of the rainbow or in a more technical term, the visible spectrum. The way we see colour is that coloured objects absorb some colours of light and reflect others, for example, a red object is reflecting red light and absorbing the rest, so we see it as red.