The colors of the frame over-accentuate the shadows being cast on it, giving it its ghostly, sketchlike (especially the BB shot) appearance.

Take a look at how the inside of the rear triangle, the top and bottom of the down and top tubes, and the sides of the seat tube are in white, while the rest is grey. Consider how the lighting hits each shot, and what in the photo, had it been an all-grey frame, would have appeared lighter by virtue of sunlight (i.e., light grey or white) - the very areas of this frame which have already been painted white.

Also, note that the shot of the 531 decal (from the front) and those of the the Roberts logos do not give off this effect, for the lighting angle is either less pronounced, or from a different angle entirely.

-Kurt