Consoleman: One explanation may be that in your photo, the camera is facing 'dead on' with almost not angle. Marla's pictures have an angle to them catching the light and fluorescence.
And then there's that whole "Variations in shade blah, blah, blah" disclaimer all the tile companies put out there!
Lighting really does change colors - all day long, especially outside. Wall paint, tile, pool finish, etc. It keeps things interesting, right?!!!