I've started month ago to try modding. I've changed few aspects of the game, but when I try to change unit's wireframe (terran unit) it appears to be multicolored (damaged) while it should be whole green (already built status). General format of wireframe is using black background, green (healthy) and yellow, orange, red (various levels of damage). I've used GIMP for edit (and obviously MPQ & GRP Conv for extracting purposes).

The extracted bitmap should be multicolored. Do you mean in-game it is multicolored? If so, use the Wireframe palette from my Palette Pack so it wont use the wrong index.