I've never used the marquis reagent to test for meth, but my chart shows that it should turn a bright orange color.
How old is your kit? I recently found out one of my older bottles went bad. Used it to test for MDMA and it turned a strange dark bluish green color instead of purple. Thought for sure I got ripped off... but I purchased a new kit just to be sure. I was pleasantly surprised and happy when the new test quickly gave me the reaction I was looking for.
Just a thought! If your kit is still pretty fresh, I'm not sure what to tell you. You could always test it on asprin or sugar to see if they produce the correct reactions.