WhineCube's framebuffer emulation is active whenever a game is started. The "green fuzz" is a YUYV representation of whatever's loaded in the memory area occupied by the framebuffer. When the game initializes the 3D hardware, the framebuffer emulation is disabled and the green fuzz should disappear.
Not really. Of course I could do it in theory, but there is some homebrew that wouldn't show anything then. Also, it wouldn't do anything for you other than replacing the green screen with a black one.