I had that experience when I was about 14 or so. Headed to London on a school trip from Dublin. We left our hotel in one of the cheaper parts of the city early in the morning, and I discovered my classmates were gaping at the passers by, astonished. I couldn't figure out why.

It was early morning down a side street, so the crowd was mainly non-white immigrants on their way to work. I hadn't noticed anything unusual: I'd moved to Dublin from London five years before. Some of the less travelled others probably hadn't ever seen a black close up: Dublin was very white thirty (Eeek!) years ago.