The other side of the coin is that there is racial discrimination by private, mostly crappy Chinese employers

It's true and it's what happens when education becomes a private enterprise and is run by people who don't know much about teaching. They are therefore forced to sell their product/service along different lines which does include (but is not exclusive to) the teachers image. In that sense it is not just non-white teachers who might be in for a hard time but also those who are overweight, old or otherwise deemed unattractive.

Black teachers can be successful in china but they generally have to work that bit harder at the start to win round local colleagues, students and parents.