It's about a "boy" maybe 18 that can jump between shadows. He finds a girl that is capable of doing this too, but she doesn't know she can. He starts to train her in how to do it.
I'd appreciate any help finding this book. I've been looking everywhere.
Could it be Shadow Jumper by JM Forester? It's about a boy who's allergic to sunlight and jumps around on rooftops.