Hi Ben and welcome. As much as I would LOVE to..I don't keep Whites tree frogs. But at a guess I would say that the brown frog on top of the green frog is a maleLol. Are these frogs both the same age? Has he got nuptial pads? (black pads on his thumbs) Males can amplex with other males so I wouldn't say that the other frog is female. They are both gorgeous by the way.