Hey Edie,
Thanks for looking. I have had trouble finding amphibian sites for maine as well. I can find sites identifying the calls, but he didn't speak when I was holding him. I googled Bufo Americanus, and that may be him. The image search showed a few similar to him with the belly but none that pale green color. Maybe he is a juvenile or maybe the color is variable. I sent the photo to a frog and toad guy at a university-- one of the toad pix linked to their site of pictures of toads, etc. So maybe he will tell me what it is. We shall see.