One of my sens was really dark like that when he was smaller and on black gravel, but now he's just got the normal coloration, hopefully yours keeps it.
Hate to bring up a dead thread, but I have to ask...
lnelms2, have you seen the color fade at all after a month? A lfs one county up (not so local I guess) seems to have a few. They are two tone, black top gray bottom, like the one you pictured.
Any signs of him graying out? I've heard some times these colors can be induced temporarily...