I'm thinking PPE or some similar morph. I've seen some that weren't as brightly colored, but lighting has alot to do with this. I do see some white spots/small lines around the upper rim of the underside. They (white striping, etc.) aren't always as big and noticable as those in the linked picture, but I've noticed some level of variation on the amount of white in the undersides across the board for Z. gigantus. Can you get a shot of them closed up? This will isolate the undersides a little better.
How long have you had it? If not long (or if it has been moved around in your tank), give a little while to settle in and take another shot. If those pics were taken with a point and shoot, maybe try putting a magnifying glass between the camera and the coral to see if that gets you a better shot. THis only works if the coral is realtively close to the glass, though. It should help get some better shots. Turn off flow and adjust white balance if possible (create custom or manual WB by using a piece of PVC in the tank or your sand bed for that blue hue) to remove the blue coloring and make the picture more realistic.
