It can be hard to tell based on color alone. Pure MDMA is a clear crystal; if powdered I would imagine it would take on a white crystalline appearance. I have personally seem MDMA that appears to shimmer, so it is possible to have a high purity white-crystalline powder. I have also seen brown MDMA of ~ 99% purity. It is possible, if the comedown was abnormally harsh that it could have been a research chemical.
To the original poster, was the duration on par with MDMA? If it was significantly shorter I would suspect Mephedrone.
Clear to white crystal is the highest purity. There is MDMA, due to the way the structural lattice absorbs water, that is brown and EXTREMELY high quality.