I think a "uniform" in a fight sport setting is just kind of silly.
It would be like having every boxer wear the same robes, trunks, shoes, gloves, etc.
No color? No flare? You mean the Mexican fighters aren't coming out with 4 flags, 10 belts and the Mexican Boxing mascot with the crazy eyes?
No Mexico Vs. Puerto Rico flags/colors in the fighters would kind of take away from the atmosphere of the rivalry IMO.
That would be tragic, and honestly I don't wish that on MMA either.
Russia Vs. Brazil could be that rivalry for MMA, let that be a uniform of its own.