lol... If you are going to a Muay Thai gym and they have belts I would find another gym.
And for belt colors I have a red TKD belt but would never think about flaunting it in the MMA world. Some day maybe after I am too old to fight I will finish getting my black belt but between stupid forms, 1 steps, point sparring and other crap involved in TKD when I am training to fight it's pretty pointless. That is all my opinion though.
The only belt I would like to work on getting and would use as "MMA Credentials" would be Gracie BJJ. I really need to start going to Gracie Barra Seattle...
"A pint of sweat, saves a gallon of blood." - General George Patton