I understand people asking the same question again and again but try to keep it to a minimum.
The DXM and MDMA reaction might seem a bit similar but once you've seen DXM and mdma you definitely know the difference.
DXM goes some very ugly brownish right away and then goes black (at lerast, that's what my pure sample did)
No purple, you will not see a trace of purple with DXM.
With mdxx, there are always traces of purple, even if it seems to go black right away (that black were talking about is actually very, very, very dark purple; so dark that it seems black)
Again, it is tricky but once you've seen it, you know.
aj