I've written before how there is a little subconscious racist bias (a term I hate when used generally in the west as it's not true) in Hong Kong. As a white westerner, I'm the second last person sat next to on a busy bus, (they think we smell, probably true as Chinese genes don't result in smelly armpit sweat), the guy with a turban is the last. Neither of us care, we have somewhere to put our bags. It's probably more that locals, and Cantonese, isn't subtle. "You're looking fat" is not something I'd say to anyone, but locals will do, not in an offensive way, but as an observation as Cantonese doesn't have such subtleness.
The government machine does treat people of dark skin as a lower class because they can (the police, immigration, etc) as often reported. But in day to day life it's probably not a huge issue if you don't let it worry you, but I defer to those that experience it who will probably see more subtle fear/avoidance/trust issues than dealing with locals or white westerners.
You have to remember that ultimately the problem is "Chinese nationality" is, but for a tiny number of people, entirely based on blood and race. British nationality is not. Leaving aside the few knuckle draggers you get in any society, calling a person "not British" because they have dark skin will get, as it should, shouted down. Calling someone of Indian, Pakistani, Nepalese or European descent "not Chinese" in Hong Kong/China because they don't look like one is locally acceptable. Calling non-Chinese race HK PRs of 10, 20, 30, 40, 50 years standing "foreigners" in HK is also deemed acceptable by the HK and mainland governments despite what the Basic Law says.