Correct, but imho you'd be mess up good weed. Anyways, just because it turns black doesn't mean it burns. It probably is just getting mixed with any tar or resin already in your bowl.
The funny thing about stims like MDPV and RCs often found in Bath Salts is that, after a couple weeks of use, especially with smoking ime, the user's subjective high (intense energy and euphoria, as an example, that were present when they first started using them) seems to diminsh. As you say, you don't feel like you're getting as high.
WELL lemme tell you, you might not actually feel it in an obvious way, but you're still getting just as stimulated and whatnot from the bath salts. Any urge to take more than what you might have started experimenting with, well, it will just make things worse in the long run if you act on it.
It might sound kinda weird, but even though you don't necessarily feel as stimulated as before, you are still going to show signs of such to those around you (although in a way, it is also because you body has become more used to the drug in it). I just remember when I was using MDPV I thought I was waaaaay less high than I actually seemed to EVERYONE around me (and I am very familiar with stim highs).
Just watch yourself (as you seem to be doing well).