Previously, somebody showed me a way to change the available colors for you and your enemies. For example, there are 12 preset colors, you start with the blue one and it would give you the whole color box and you could directly change that blue to any type of blue (or any color). Then that would be the new available color to choose (it replaces the original preset color).

I am no longer able to find the way - I thought it was in the avatar modification screen, but they changed it from before. So does anybody know how to do it? Thank you!

Settings > Accessibility > last button opens the palette. 

And if I may, enabling 20 colors would be a very nice and (I suppose ?) easy addition in terms of replayability, since players who tend to like full maps often run into the same colors from one game to the next with only 12 slots. 

Thank you very much GCX. That is what I was looking for.