I have some 4-AcO-DMT (supposedly) that is basically dark brown or even black flakes, I don't know what this means but I am still able to crush it up and insufflate, and I have always got strong effects from it. This has lasted me a while and honestly I've never known any different so I've never tried any sparkly clean powder that I see people talking about here. I do however get a sort of bodyload, I think, and not breathing difficulties as such, but possibly some extra mucus production in my nose, extra saliva production, etc...
To be honest I think that I got this on old school psilocybin mushrooms too, so I never really paid it much attention, I thought maybe this was just something about psilocin analogues, although thinking about it now I don't think I get this from metocin, or at least if I do, it's to a far lesser extent... and what I have of that looks a lot cleaner and what you would expect for a fairly pure substance in powder form...
After a while typically this stuff levels out and I've had some beautiful and profound experiences on it. But I'm thinking now could this be a mild allergic reaction of a sort? I'm not sure... would like to know what the colour means though as far as degradation and whether I should be concerned...