how to sex them:
males - first sign when they are babies their insane growth rate, by insane i mean it, they can easily double their size in a matter of 2 weeks when they are still tiny, provided they are fed and housed properly. When they are about 3-4" you can start making predictions with more or less certainty.
males will have a bigger, wider heads, it is not uncommon for a head to be 1/3 of a body at that size. and the most guaranteed sexing method is to hear them call.

females, slower growth rate, head is more narrow and small in comparison to the body and of course they don't call, adult females are smaller then males.

it is common for both males and females to have brighter coloration, that is no way to make assumptions about sex of a frog. both genders can be very bright or have no yellow ( or almost non).