Lembro-me de ler uma história uma vez em que todos havíamos cruzado, de modo que não havia mais negros, brancos, asiáticos etc. etc. Éramos todos "pardos". De alguma forma, eles 'encontraram' crianças 5 que eram 'raças' de raça pura, e eu não me lembro de mais nada.
Eu acredito que isso pode ser de Piers Anthony Race Against Time conforme minha resposta aqui.
Vou apenas citar o texto:
It involves a 20th century white boy accidentally scratching off the skin of his friend, showing that it's all brown underneath, and that there's some vast conspiracy that everyone but him is involved in. I want to say that his friend still helps him, but the majority of it is him corresponding with a penpal through coded letters (they do something like having the message be in every third letter) to escape and find more people like him.
Of course, the reveal isn't that the people around him aren't human, but that
[Spoiler à frente]
The human race has become a homogenous brown due to the mixing of races here in the 24th century, and the protagonist, his pen pal, and a few others are genetic throwbacks to earlier races being preserved in a zoolike "natural environment".