[trunker]

They will just assume that you are from where ever it is you are coming from, ie if you fly over from the US, then you're american, UK british, etc, etc.. they will think of this first, and you will be categorized as such, and then as a second thought they might be curious about your heritage.

in which case follow C.

and while you may have korean blood you would still be first and foremost american or british or whatever, so dont worry about it, tell the truth and enjoy your trip.