Many people ask this question, and the answer is quite simple. We are not talking about the mixing of colours, which is what a lot of people base that question on. All colours can be mixed in different ways. But there is only one way to perceive a colour. A pure green is not yellowish or bluish. It is green. All elementary colours can be defined in the same way. An orange colour, however, will always be both reddish and yellowish.