It's SF so ANYTHING goes, IMHO.
If I recall correctly the AT-AT's in all the movies were a light-grey not white, but than most of their walkers and space-ships are either a light-grey or a blue-grey.
Go with a camo-scheme and feel free to mix colours to suit an ALIEN environment like blue and purple, yellow and green, etc.
The way I see it the SW Universe goes way beyond what we see in the movies.
HTH.
P.S.: I have seen even a pic of an AT-AT done up in German WWII markings in a pic(methinks it was on FSM too)