Marked vs. Unmarked

I first realized I was marked/unmarked when applying for college and being asked my race/ethnicity. I am from a very homogeneous part of the country, New England, where it is assumed you are a white Anglo-Saxon protestant. Marking "white" on my college applications was the first time I had to define what I was. Of course I knew that I was not black or hispanic and have many friends who are not white, but this was the first time I had to definitively mark what race/ethnicity I am.