Why Do We Think of White as a Pure Colour?

We always used to think of blue as the thing that was a long way from us. The great irony is, when we finally actually got up into the sky and we went up into space, we looked back down again,. We realize that actually the earth is far more blue than it is earth coloured. And next, i wanted to ask you about white. Why do we think of white as a pure colour? Yes, it's interesting. It's one of the most universal color connotations out there, is that people all around the world associate white with purity. But in some ways, there is a physical basis for it. I guess, in white is produced by a a process that