If you switch the View to Status, all pixels will display as black, white or gray. Black pixels are completely transparent. White pixels are completely opaque. Gray pixels are see-through (partially transparent/partially opaque ). This view allows you to easily see problems in the matte. In general, it's good to have some gray pixels around the edge of the foreground (so that hairs and other semi-transparent elements can blend into the background), but the background should be solid black and the foreground solid white.