Most zeds seem to have telltale ways of distinguishing them from eachother, unlike the old KF mod where everything looked the same except in size.
If you go with a sort of fur look and make it fit in then the Brute probably wouldn't need any other distinction, but if it's hairless that might be a bit tougher.
Clot = white
Bloat, Siren = yellow
Crawler = black
Gorefast = red
Husk = brown
Stalker = transparent, white
Scrake = blue, white
Fleshpound = light on chest and back
So maybe it could just have an odd skin color, or marks like bruises all over his body? Just throwing out ideas - and sorry for the loose pronouns, never sure what to call specimens.