@HorsesandMuchMOAR  
Good thing those are changeable

@Prometheus labs CEO
 
Most likely. They can tell if someone is from another place by their dialect and customs.

@HorsesandMuchMOAR  
So instead of racism theyd have nationalism/nativism, at least it’d be really hard to tell if someone is from one area or another, making nationalism very difficult

@Prometheus labs CEO
 
The most obvious sign could be their family background, and also the sense of community felt by a group of inhabitants. So unless any of them would object, or say “I’m from that group”, we may assume that “most residents of Canterlot/the main area where EqG is situated are ethnic Canterlotians”.
 
Even then, EqG people/Canterlotians would be different from us humans.
 

What exactly constitutes ethnicity in a world where everyone is a different technicolor

Oh, yes, I do. Either you’re East Asian (most likely Chinese like me – on the other hand I don’t like it if people think I’m White or Black, but I don’t get so mad, and you could enjoy our culture if you wish) from your appearance, or you’re of the humanoid Equestrian species (of the Canterlotian ethnicity).
 
I hope, Mr. Sentry, you do not mind that regardless of what humans do you resemble, you, your purple girlfriend, and the rest of your people are considered to be a different humanoid species from us human beings. After all, we humans are not born with green skin or purple/pink/blue hair, and you would be an interesting case on studying about alien life.
 
Mr. Sentry, would you like to volunteer for a scientific study of your extraterrestrial people’s genetics and society?
 

Sorry, bruh, but you sound Green.

Are you saying you aren’t Orangarian?