Hi Georgina, I've just read your excerpt. I don't think it comes across as being particularly racist, but perhaps a rethink on the way it's worded might help. We are all especially sensitive about giving offence these days, but in my view, if the encounter is sensitively portrayed so that there are no misunderstandings, I see no problem. These things need to be discussed openly, but with care. I was born in Paddington - a long, long time ago! - and there was a lot of racism then, not only people with dark skins, but Jews and foreigners from all over (even Scots ;-) ) but there were also some really nice people form all backgrounds.
Mistakes happen, even when "colour" doesn't come into it. What's important is how they're dealt with. Try to see things from both sides. I'm sure you'll work it out!