From my days peering into the night sky, red light did not destroy your adapted night vision that can take 15-20 minutes to acquire, whereas other colours did. Kind of like a dark room I guess.
In a 172 with steam driven instruments, a red light might useful. When there are several 8inch square multi colour PFD/ND displays in front of you I don't think your eyes are truly ever night adapted so a red light would be rather pointless IMHO.