I was wondering, where did this coloring scheme for rank and ratings come from.
Almost all OJs i know, follow the same color gradient which goes from
Dark, Green, Blue, Orange, Red
(and some variations like cyan)
This is used by all popular OJs like Codeforces, Codechef, Topcoder, Atcoder.
Does this coloring has some meaning as well, because all websites are using it.