In my experience "kolega" has a very wide use in Poland and does not equate to "colleague". In English, we don't talk about colleagues from school or university, for instance (unless you're staff). And in English we don't necessarily like our colleagues, just work with them.
True, but I would add that you don't have to like your 'kolega' as well. If I met someone from my school on the bus, and we started talking (for the first time ever), and then we met my mom, I'd say "Mamo, to jest Paweł, kolega ze szkoły". The word 'kolega' can be really... meaningless sometimes.
The problem is that 'colleague' in English means a co-worker, which is different from Polish 'kolega'.