It's a male spicebush swallowtail. Male spicebush swallowtails usually have a blue/green/silvery wash on the topside of their hindwings, but I have some that have a mint green wash, the same color as their mint colored lunules. I've read that I have two types here, the regular spicebush swallowtail and the coastal spicebush swallowtail. I'm thinking that the one with the green wash is the coastal type, but I'm not sure.
Here's a picture of a male colored something like yours -
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And here's a male with the green wash - a coastal spicebush male?
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MissSherry

Yeehaaaa! (That's Southern for woohooo!) I knew if I could catch MissSherry online, I would get the answer right away.

Didn't you point out last year the distinctive pattern -- a missing orange spot -- on the underside of the hindwing? I had both Audubon's and Peterson's field guides open to pictures of the black swallowtails, and that pointed blue cell third from the left is the only thing that gave it away.

I found some blackform female Tigers hiding in that folder, too. I've got to look at these pictures more closely when I take them off the camera.

No, Geni, black swallowtails and spicebush swallowtails look so much alike on their undersides, and they're so different on their topsides, that I've never even tried to ID them strictly on undersides.
MissSherry

MissSherry, I apologize for misattributing that to you. I wish I could remember who pointed it out. It was one of those lightbulb moments for me. Here's a closeup of the spot I was talking about.
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He He He , after all this time I checked out this post.

I think it might have been me to point that out. Ever since I learned that bit of info, I've never had much trouble telling them apart. But there are always so many subtle differences in species that are hard to spot in the beginning. And once you learn them, you wonder how you could have ever been confused.

Maryann