Hello.

Thank you for the report. It's a very common situation even on real weapons and it would be strange to unify colors on our weapons or to name colors like "sand", "light sand", "lighter sand" and so on. There are many RAL shades of the same color used on real weapons. Yes we understand that from a perspective of a gamer it seems odd, but the game is trying to be as close as to the real situation in the real world.

Useful references:
link 1
link 2
link 3