I can't think of any reason why there'd be a problem with reskinning / recolouring some of the existing models (like robes) to add more colours - it's easy to make (just hue shift part of the texture), and as far as I can tell, would be relatively easy to implement in game.
If the colour exists on one of the other
items of clothing, it's probably fair to say any other "shape" of clothing could be that colour too if it's wanted - i.e. normal guy in town has a yellow top and grey trousers, "hillbilly" has a green top with a brown waitcoast, so any other cloth can realistically be yellow, grey, green or brown without looking wrong.
Technically, I can't see any problem with doing medic armour either - again, just a reskinning - though the logo part would probably need to be much bigger. Of course, ultimately it's all down to dev's decision whether they want / need any of these in game.
