I am somewhat colorblind, so the answer to this question may simply be that I don’t see colors the same as most other people.
When I see something purple, it looks to me like a combination of red and blue. When I see something orange, it looks like a combination of red and yellow. However, when I see something green, it looks like a totally different color. I don’t see it as a mix of blue and yellow.
So, basically, the question is, do other people have a similar experience? If so, why would this be. [I note that most games that have four colors have red, blue, yellow, and green. So that does make me suspect that green is more distinct than orange or purple, but maybe there is another reason.]