Anyone who aspires to be a white ally to people of colour must read this book. It was published in 1963 and I wish I could say it wasn't relevant today either in the US or the UK. But it is. Still. But one way to make it irrelevant is to read it and think about (and later, act on) what Baldwin has to say. For instance, towards the end, from pages 81 & 82: 

A vast amount of energy that goes into what we call the Negro problem is produced by the white man's profound desire not to be judged by those who are not white, not be seen as he is, and at the same time a vast amount of the white anguish is rooted in the white man's equally profound need to be seen as he is, to be released from the tyranny of his mirror. ...

It is for this reason that love is so desperately sought and so cunningly avoided. Love takes off the masks that we fear we cannot live without and know we cannot live within. I use the word 'love' here not merely in the personal sense but as a state of being, or a state of grace ... in the tough and universal sense of being and daring and growth. 

People who cannot suffer can never grow up, can never discover who they are.