Callum by Malorie Blackman

In a world where dark-skinned Crosses rule over light-skinned noughts, a nought boy clings to his forbidden childhood friendship with a Cross girl as they navigate school, prejudice, and rising political violence. When he gains entry to her elite school, relentless discrimination and mounting tensions pull him toward risky alliances, forcing them both to face painful truths about loyalty, love, and the brutal system determined to keep them apart.