Brightskins wouldn't be that relevant, really. The big honking red letters over every enemy are usually 'hint' enough that they're around. Even with stealthed players it's not going to have much impact; when you hear the sound it's quite obvious there's one nearby, and they're quite easy to spot regardless. More to the point, it's both completely impossible to detect as their current system stands and so easily fixable to prevent this kind of stuff (load only from the .mpq files, run checks on their veracity - you could go around that fairly easily still, but meh) that any kind of action is unlikely.
I'm looking into the system that they use to create their textures, and although I haven't checked I'm pretty sure that I can edit them fairly easily using Photoshop or similar. I'll run a few tests if I have the time this weekend to see if I can just edit the existing models; making further changes from there would be the next step.