Noughts and Crosses by Malorie Blackman 

Sephy is a Cross: dark-skinned and beautiful, she lives a life of privilege and power. But she’s lonely, and burns with injustice at the world she sees around her. Callum is a nought: pale-skinned and poor, he’s considered to be less than nothing – a blanker, there to serve Crosses – but he dreams of a better life.

They’ve been friends since they were children, and they both know that’s as far as it can ever go. Noughts and Crosses are fated to be bitter enemies… Read more.