I found this game while lurking on Newgrounds which employs a strange concept; I'll try to explain it, but it's much better experienced firsthand.
Basically, you and the walls are colored black, while movable areas are colored white. However, hit the left shift button, and you'll "flip" around, and the colors are reversed; you are now white (lol racism) and all white blocks are now obstacles, while black areas are empty. Sounds a lot more complicated on paper than it actually is.
The author also pays tribute to Portal throughout the game, and it's just as addicting, but incredibly short. He says he's willing to make a sequel, though.