I've heard it a couple of times in the last season, loud and obvious and directed at other fans, but unfortunately it was people behind me and neither time was I able to work out who it was. Many other fans will have clearly heard but nothing happened. Both those incidents were guys being aggressive to Asian fans, with the suggestion they were not proper fans, and made direct references to their race.
For players today, then clearly it's not constant bananas and monkey chants like in the 70s - it's probably something a bit more subtle that one person will see and others won't. Yaya, Sterling, and Mahrez got a lot more questions about their attitude, and were often referred to as lazy. Now there are probably times they did have a bad attitude, like all players, and no doubt many on this site will argue race has nothing to do with it, and for many fans it doesn't. But If City or England lose then the abuse is disproportionately directed at the black players, even if most people are self aware enough these days not to use racist terms.
I don't think Mahrez got as much abuse because he wasn't white as Sterling did, but I loved him as a player, and at times he dragged City to some big results. He may have had off games, but Kev plays a lot more FFS balls, than Mahrez did (because that's the nature of trying something special), and I didn't see a player that hid, any more than others when things weren't going well. Yet he is still given more grief for his attitude, and for being lazy, than most players.
It doesn't follow that all of the people that think that are racist, because every fan has their favourites, and players they don't think are up to much - but that's the kind of abuse the racists amplify and the kind of abuse they hide behind. We know there are millions of racist people in the UK, so of course there are plenty of racist City fans.
ps. that might have been a bit rambling - struggling to type at the moment, as I've just dislocated/fractured my shoulder, so just pecking it out with one finger painfully.