Now this won't concern most players, but it would be an extra incentive to get Master if you could change your [MASTER] tag to any color you wanted. Just like how /name or /tag (For MEGAs) works now.
Whilst I find this an interesting idea, I don't see it as necessary as MEGA's can already change their tag colour, and donors can change their name colours. I think each build rank is better off having its own specified colour, makes it easier for newer players to remember which rank is which and makes things like master warp displays easier to build.