I know the professor who writes this blog, Bill Gasarch. I was thinking of interning with him (at our high school, we do an internship + report about it in our senior year), but then decided against it because the math is a bit too abstract and unapplicable to (as Gasarch would put it) make me "properly enthused". He seems like a great guy. Anyway, while I haven't read the entire thing, I would suggest reading the book he has online - it's quite interesting, and it goes into more detail about colorings and such, so anyone who likes this post will find the book interesting as well.
Combinatorics isn't, but... coloring grids of squares?
Not that I really have anything against abstract mathematics. It's still very cool, but it's just not going to get me very excited - or at least this exact branch of it, I guess.
I'm not one to say that coloring grids of squares sounds fascinating to me, but nandemo's point still holds -- as far as mathematics goes, it's pretty concrete.
The opportunity to work directly with a university professor while still in high school is fantastic. Wish I'd had it. I hope you ended up taking advantage of it with someone else. Even if you're not totally absorbed in the research, this will give you a huge leg up when you reach college.
Living near the University of Maryland and NIST and etc, there really are a bunch of opportunities to work with professors and researchers in high school - it's really quite great. I hope (slash think, but knock on wood) that I'm going to be able to work with either another math professor or a theoretical physicist over the summer. :)
Yup, it's the Montgomery Blair High School Magnet Program - it's in Silver Spring, Maryland. The funding cuts are kind of hurting it, but it's a very good education, especially if you put your own effort into it too.
(Are you, perhaps, somehow associated with this or another magnet program in the MD area?)