to see how to make the gray fade away (floor):
after doing the the gray layer, create a new layer over it.. put some white (with the brush) at where it should be white (duh) thus at the end.. then lower the opacity of that layer. then take the smudge tool, and smudge the white toward the gray part (always on the white layer of course).. to make it uniforme, smudge the white that's in the gray part from right to left with lower strength (like 20% or so)