Green Tree Frog Colour :)

[Frogs1]

Hi, I'm just wondering why one of my whites tree frogs is always a lot darker in colour then my other one? Is it lack of calcium, or something else? Or is it normal. The lighter colored green one goes the same colour during the day as the dark one, but at night goes lighter but the other one says the same all the time.

Is there anything I can do to help it go a lighter colour? I like the lighter colour more then the darker colour :P thanks for any help. (Also I don't think I have ever seen her go light green, I have had them for a month)