As for the colors, I consider that the current system is fine, because so far I have not seen them repeated by more players than there are. Also, making colors free is great because it fuels the creativity of the players, at least in my case seeing and having so many colors makes me feel more comfortable with the game. On the other hand, if you get to sell and buy colors, wouldn't it be annoying to have to fight someone who has the same color as me? How could it make a difference at the top?
What if I am a clan that wants to attract attention to attract members but there are other people with the same color without being from the clan?
The same if I am a streaming or if I want to generate a trend.
As for the possible change in the tag's, I really do not consider it a great idea, since it should be considered that there is the option that is on the right side of the tag (pin). It would not be better to strengthen that option so that even if they get my tag they cannot access it without my pin?
This is my humble opinion.