I was looking into this for my KV-1 and this statement sums up what I found:

"The Red Army preferred its armor painted olive green and you won't have problems finding this color in any store. As an alternative, you can use olive drab which looks very similar. Testors Model Master makes a color named "Russian Armor Green" which is almost blue. Most modelers have no idea what that color is and why it's so blue.

Olive green was the predominant color throughout the war but it was impossible to guarantee regular paint shipments to tank factories so the assembly lines often used whatever green was available. If some kind of tractor green was the only paint in stock it was applied without hesitation. Some tanks were not painted at all due to lack of time. A few tanks had a brown camo pattern painted over the olive green but this was applied in the field by the crews and there was no specifications describing it. If you want to try it your guess is as good as anybody's."