The person to ask if these are really axanthic would be Tom Crutchfield given he does breed true axanthics (among others).
The iguanas they are selling at Petco labeled "Turquoise iguana" or other such colorful names, are ALL imports and they canNOT guarantee they will keep their color (even regular green colored green iguanas can vary a bit on their coloration as they reach adulthood...to guarantee a baby will keep that same intense green even is a farce unless it is a specifically bred trait like Tom's iguanas). I inquired on them to find out where they were getting off calling them something they are not.
What I can guarantee, is they are the same species, Green Iguana (iguana iguana), period. Just like the red iguanas, they are all Green Iguanas, the same ones that get dumped all too frequently.
In all likelihood, this blue will fade as they mature. The only way to tell that is to raise them up. These imported colors are still just from local specific and possibly dependent on what they eat (it depends on what you're asking at).
They still require the same advanced level care that any Green Iguana does however.
Kindest regards,
Amanda Rose