ok, I see a pretty compromise in this idea actually. We do know that the ATSTs on endor were plain grey metal. Thats a fact, we know that the empire isnt really fond of camo... Look at the stormtroopers for example. But wedo know, the rebels are big fans of camo. So if you had a scenario on a forested/jungle planet where rebels had stolen some ATSTs or captured a small base, you can justify the camoflauge of the ATST, but only for rebels.

The only difference I would really like to see in the skins of the ATSTs for imperials, would be some battle scars (slight ones) and different colors on the feet, endor should ahve brown/green, Hoth should have a little white, Tatooine maybe a tan color of the dust in the air all over it, stuff like that.

But imperials were not draping moss from the legs of thier walkers.

"Munchkin: One who, on being told that this is a game about politics and intrigue in 17th century Italy, asks to play a ninja."
— Andrew Rilstone