As for point by cavortingcheetah, I would say that only a very small minority of expats lack in competence and aptitude. But, if you are "bottom feeder" airline with smallest salary and otherwise worst terms and conditions, you will get pretty much all of the not-even-upto-your-standard expats to your doorstep. Hence for example Turkish will be screening many more bad apples than emirates.
I've never before heard that expat is skin colour thing. According to the grapevine KQ union doesn't like the idea of expats even if they would be from Tanzania and Uganda.. Likewise I haven't heard Kenyans on any colour having any easier time in ET assessment than Caucasian or Indian applicants.