Just so p[eople know, a colour impurity can mean anywhere from 1% to 99% of impurities. Sometimes a powder can be off white or beige or something else and still be 98-99% pure.
But in the word of meth, speed, base, ice, whatever form your meth is in, 99% or even 90 or 80% isn't going to be anywhere near what you're dealing with unless it came from a professional real commercial lab that sells to people with licenses only. Its just not in a cooks interest to make a product pure.
I have seen a giant bag of brown base, that was pretty good. Stimulating, but a bit of a chemmy rush if that makes sense, I don't know if its adfulterated, and this stuff was cheap so I'm guessiong dealers are crystalizing it to sell it for double the price as ice.
But I would put my money on the stuff being oxidized a fair bit from a non-washed phosphorus-iodine reaction at synthesis. And the oxidisation made the purple appear more brownish. It would expplain the rush from IV and probably smoking too as iodine has been known to change some drugs when the impurity is leftover in it, normally making it more stimulative, and can even change the high a bit after the rush, headaches and even inflammation pains may increase. It worked that way with 2C-I anyway