Fair enough, if synth process and the cleaning/washing process doesn't affect MDMA's colour, what does?
The color is caused by the presence of an impurity.
It's possible for an impurity in very very low concentration to cause coloration, so the presence of a color does not necessarily indicate a poor quality product.
As to where the impurities come from? There are several possibilities. Synthetic biproducts leftover from inadequate purification steps are common in street drugs. This has to do with the lack of proper lab equipment (good vacuum pumps and distillation glassware are expensive), and general economic factors like minimizing the use of expensive solvents for trituration, extraction and chromatography etc. Other likely culprits are the quality of starting materials/precursors and reagents which can themselves be impure. It's also possible that someone could add another substance to MDMA as a cutting agent: the cutting agent could be considered an impurity, or could itself be relatively impure and the source of coloring.
Generally, as organic materials age, they develop a yellow-ish brown-ish color (like old paper for example). The reason compounds tend to turn from white -> yellow has to do with minor amounts of decomposition products forming over time (giving very stable aromatic products that are highly colored even in very low concentrations) These aromatic compounds are good at absorbing UV light, and as they accumulate, they pull a little bit of purple light out of the visible spectrum leaving you with yellow as the observed color.
^^a bit long-winded, but another source of coloration caused by impurity could come from aging/decomposition of the material.
K-Dazed: I apologize if I come across as condescending. You're mostly correct in regard to the general idea of your posts, but as they say "the devil's in the details"
Color indicates the presence of an impurity. However the absence of color does
not indicate the absence of an impurity. Highly colored material isn't necessarily THAT impure (can still have colored material that is easily 95% + pure). The bottom line is: you can't estimate purity from appearance/smell/taste. Get a test kit and play safe
