I need your help!

Whoever told Ты brown hair doesn't dye well purple, they weren't saying truth. my friend naturally has mid-brown hair and she dyed it a subtle purple color, and it looks ah-mazing. That kind of thing you're talking about would probably apply to people with say black hair trying to dye it light blonde.
on the side of the dye box it should Показать a color spectrum of how it's expected to look.
If Ты want purple hair, go for it. go for what ever color Ты feel like, then Ты will be less likely to be disappointed. don't worry about what anyone else thinks, cos I've seen it on brunette people and it looks fine :)
It would help if when Ты wash your hair the день before Ты dye it, that Ты use a deep conditioner to make it in good condition, then the result will look better.