It can be fixed but requires a little knowhow on how to edit the handling.cfg file in the GSX folder,
you need to go into notepad and change every instance in the handling cfg where the colour is white, you need to change it to cool_grey (or cool_gray, I can't check right now)
Once that's been done, save that file and your vehicles will no longer be black.
The downside to this is that it requires you to do this step everytime you update GSX, because the cfg file gets over-written with a new one.
