I'm afraid that this is a Madagascar Giant Day Gecko (Phelsuma grandis or P. madagascarensisgrandis). Standing's Day Geckos are about the same size, but they don't have any red spots and other overall color is more of a blue-green than a bright green). Maybe the tank was mislabeled or individuals of both species were in the same tank. The calcium sacs on this individual are so large that I would guess that this is a female.
