I'm pretty sure those greener non-snow terrain was custom. In any case, they wouldn't give much advantage to tan color. MO on the other hand uses a more vanilla-esque terrain aside from Desert. Desert terrain in Mo itself is enough justification why Tan would be very advantageous in minimap
That is true...your forces would be invisible to radar. A few Empire at War mods had that issue: Black was a color you could pick, which made the Empire look much better, however because you're in space, your fighter icons were hard to see in the backdrop, and I couldn't even tell where my own forces were half the time. I can see the reason behind why Tan isn't used, a shame, but understandable.
Regarding Russia, I think the LC should get the Shock trooper and lose their Tesla Trooper. Honestly, Russia is boring and very basic; they are a tutorial nation for the soviets if anything.
If Volkov and Chitzkoi are literally the main highlight or "what one looks forward to" when play as Russia? Thats pretty bad. It means the rest of their army may as well not exist.
Plus while Volkov is easy to manage, you have to worry about where Chitzkoi is, as he just runs after enemies like they are scooby snacks. Its very distracting to keep track of both heroes.
This is why in my opinion, the Latin Confederation and China are a lot better with their heroes -Morales is easy to track for the player since they sit back as a sniper, and Yunru is a mostly support character (who also can destroy buildings too).
Personally, and I've said this in a different post, Krukov and Reznov are much easier to manage and keep track of, since they are a better "dynamic duo" and have their own strengths and weaknesses.
More or less they are a "weaker" Fin and Alize for the Soviets. Which coincidentally, would help prepare you for playing Haihead, since they too have a "dynamic duo", that are also easier to keep track of.