Traditionally, they use brighter colors, likely to make them noticeable. There IS a Violet Ranger, though, in Jungle Fury. There is also a ranger with orange as their primary color in S.P.D, though they only appear in the episode Katastrophe. 126.96.36.199 06:44, May 10, 2011 (UTC)
They tend to stick with the traditional colors(red,blue,pink,green,yellow)although there is one purple ranger in jungle fury(R.J.)and 2 orange rangers(Kat from S.P.D.) and some orange on Dominick's costume from jungle fury). As for the gray, no clue.
Might be something to look forward to in the future.