Roleplay and cosplay are two different things, you know. Anyway, I've seen a lot of people say "go ahead and cosplay nonwhite characters, just don't do blackface/yellowface/etc and be respectful to the culture" which is reasonable enough to me.
Also, what you need to understand is that a piece of clothing is not always just a piece of clothing. Take the Plains Native American war bonnet, for example. Just feathers affixed to a leather headband, right? Nope. It has a fuckton of cultural significance, and just wearing it as a cool fashion accessory spits on that. That's the point. There's a difference between someone respectfully wearing a war bonnet while communicating with Plains Native American people and understanding the significance and dressing up as a Sexy Injun on Halloween, you know?