I really enjoyed reading Trager's post, because she and I seem to have a lot in common regarding the appearance of characters in our young adult novels. I, too, find myself thinking about personality and interaction between the characters first and what they look like second. That said, my MC's appearance is based on her ancestry.
Her forefathers (and mothers) would have come from the west coast of Ireland. I think she will be Black Irish, which refers to her dark hair and dark eye color, not her skin. Legend has it that the people from that region with these genealogical traits have the men of the Spanish Armada to thank. Twenty ships wrecked off the coast. However, historians believe that none of the survivors were allowed to live long enough to cause any, shall we say, mischief. They do think it's possible that Irish chiefs employed Spanish soldiers around the end of the 16th century. These men certainly could have, um, stirred things up in the genetic pool. Another option is that folks from the Iberian peninsula simply migrated 2500 years ago, but frankly that option isn't as much fun.
I think in general much like it has been a challenge to remember to include setting as I tell my story, since not everyone has been to Wildwood (yet), I also probably will have to go back in the end and rework in details about appearance.
BTW: Thanks Robin for sharing your story of Fluffy Kitty earlier in the week. It served as a good reminder that particularly in picture books writers don't always have the last say. I found extremely interesting a conversation that took place earlier this year via our chapter's SCBWI listserv. There was discussion of a cover controversy related to a book called Liar by Justine Larbalestier. Please check out her website http://justinelarbalestier.com/blog/2009/07/23/aint-that-a-shame/#comments to hear about her experience.