They can be kept together in a 75g together, though some have noted that C. rubriventralis can be aggressive toward other fairy wrasses, my own experiences have not shown that to be true.
Yes, C. rubripinnis can often appear to be more of a dark orange, and as far as red fins both species Latin name translates to such a meaning. Rubripinnis = red foot and rubriventralis = red ventral fins.