It is absolutely not taboo to define yourself otherwise, such as by your job, hobby, state, country, etc… but the reason skin tone racism is such a big thing is because that’s what the racists use. Where in other countries it can be more about certain ethnicities regardless of skin color, in the US your skin color was enough to make you a slave or a free man and our racism is based on our slavery. We spent hundreds of years justifying skin based racism and that pseudo science and twisted religion doesn’t just go away like a light switch.