As a British (English) Asian Pilot (now who's being PC??) who works for a large UK Jet airline, I can happily report that I have not felt a jot of racism from my fellow pilots, in general I have found pilots to be very tolerant and open minded. I believe this come from pilots generally being well educated and well travelled.
As for positive discrimination I'm not sure about that, you still have to meet and exceed the standard in flying and personal qualities to be selected and succeed in a very competitive industry.
Apart from the occasional thoughtless remark from the girls post 7/7 the airline staff are very colour blind. I have noticed the odd dodgy look from the pax but nothing to really get excited about.
So in summary don't let your background bother you just strive to set a very high standard and let your results and abilities talk for you.