As a graphic designer who uses Photoshop a lot, this photo is definitely over-saturated. Some of the tell tale signs are the yellow that is blown out -- appears blurry when it shouldn't -- as well as the artifacts (black or multi-colored speckles) that are vey obvious around the mouth.
Photographing against a black background doesn't allow for a typical white reference of egg-crate or sand as Minh pointed out, but also allows for saturation to be applied without changing the background.
That said, here's a photo of a mertensii that landed at my LFS and it looked very much like it did in the photo:
I'm hoping the person who bought it starts a thread on it -- he's active on the boards. :dance: