It was boogyin' around in the thicket at the bottom of the yard, whatever the heck that stuff is. At first I thought it was a towhee, because it looked dark up top with a bright white spot at the lower edge of the wing. Then I realized it was solid white underneath, and had a pointy li'l warbler beak, and it was anyway way too small to be a towhee.
Then it flew off.
It didn't look terribly blue to me, but having looked up photos, the blue can go to an awfully deep grey, and it was in shadow. It's the only dark-topped warbler with a white breast and prominent white wing spot in the book, and according to the charts, they're migrating through Raleigh pretty much right this minute.
I'm gonna keep an eye on the backyard before I get too excited, but this may actually be bird #100 for the life-list.