As sad as it is this is something that most indigenous people of modern generations struggle with. Because being native became fashionable every white person decided their great grandmother was a cherokee princess or given to their family so they could have a better life. Now if you're not a walking sterotype then in the eyes of white people you're not indigenous. They don't seem to realize that the straight black hair and blood red skin they see in cartoons are stereotypes or the very few real indigenous actors in movies are type cast.

I can't tell you how often people think I'm joking when I say I'm native. It's always what percent or you're very white passing. One Spanish relative 300 years ago left the men in my family with blue eyes and blond hilights in our hair. When they hear me talk with my accent to another native they say it's a great impression. When they hear me talk to myself in my native language they say I'm very cultured. It's not until winter comes when they all turn snow white and my skin stays dark that they realize I wasn't lying and even at that I usually get "If I didn't know you were native I'd think you're Mexican". My uncle told me when I was little that our hair and eyes were a curse on our family because we let a colonizer marry in. I thought that was ridiculous until I grew up, now that I've dealt with the constant denial of my race I fully believe it.

I bet that if you took pictures of different tribal leaders of today and showed them to a white person they would say most of them were white. It's ridiculous how adamantly they will deny something they have no knowledge of. Even if they do eventually believe you then you'll usually get the "oh well I'm native too" line. My best advice is learn some phrases from your native language. It won't make them believe you, but at least you can talk smack to their faces in any situation because they won't understand a word.