Isopropanol and butanol suck for preparing large quantities of methylamine hydrochloride (but do work well for high purity crystals), and as other members have said, search for my posts about using methanol to recrystallize the methylamine.
And to answer Rhodium's question with respect to methylamine (and not to MDMA), the crystals are still nice and white (I'd post a pic of some crystals I prepared ages ago, but I don't know how)
I have noticed that my MDMA discolors with time. I don't know what causes it, but I doubt it's the acetone wash.