Wally's Kid Flash costume was originally identical to Barry's costume, just smaller (for obvious reasons). The during a story where Barry developed psionic powers, he altered wally's costume to be more of an inverse of his own, and opened the cowl to let his hair through. Wally had been wanting his own look and kept the new costume (It's possible the costume was based on Wally's mental image of his possible new costume)
Zoom came along many years later, and since Wally was there first, I imagine he saw no reason to change his costume because of THAT lunatic.