So, the author creates a fictional world that is quite racist. As a little touch, the blacks are the upper class and the whites are the mistreated lower class. See, that can open up our eyes in case you're too insensitive to understand racism if the victim is black.
I have not read Checkmate but I did read Ms. Blackman's award winner Noughts and Crosses. Checkmate sounds like an extension of the world created in Noughts and Crosses.
Noughts and Crosses reverses race roles between blacks (naughts) and whites (crosses) in (it is implied) an alternate England. Callum and Persephone, the star-crossed nought and cross, struggle to get past the segregation taboos. The idea, intriguing and rich with possibilities, was unfortunately not as well executed as could have been. About half way through the book there is a huge shift into preachy clunkiness that no longer engaging characters can not carry. The earnestness of young love and struggling against your parents' prejudices gives way to victim mentality when young Callum joins an IRA-like "liberation" group and bombs a mall. As if killing innocent shoppers is justified by racism. Sorry.
It's as if Ms. Blackman can't make a story about teen love and race relations but must instead hammer in a justification of violence or at least a glamorization of it- even destroying the nascent romance between the principals by an attempted rape scene. A lot of my reading circle raved over Noughts and Crosses, I thought Ms. Blackman's heavy handed insertion of the victim mentality ruined whatever legitimate arguements she had at the beginning of the book. The most thought provoking part of her book was the afterward, where she speaks about the peripheral treatment given many historical figures in textbooks because of ethnicity.