With the pure white one you'll have to wait for it to crow (or croak, might be a better description), tidbit or lay an egg.
You might be lucky that the silver/whites (sounds like silver tuxedos) will get a few pink (in silvers the rust red gets diluted and looks more light pink) feathers if the silver color gets close enough to the tail - otherwise it's the same as the white.
If you place each of them alone with one you are certain is male in a few weeks, that might provoke them to start 'croaking'.
Most of the sounds males and females make are similar and hard to tell apart, but when croaking (a quite low sound, like quaarrrrrk) the throat gets all filled with air and I have never seen a female do that.
Males usually only do it to attract females though, which is why I suggest you place them with a male to make them do it -if there are already females around, they are not as likely to do it.
If placing them with a certain male to make them croak doesn't work, you can try placing them with a certain female to see if they'll tidbit - holding a piece of food in their beak while calling the female with a series of low peep-peep-peep-peep's. Females do this to their chicks, but I've never seen one do it to another female, so if the bird does it you are pretty certain it's male.
If that doesn't work either, you'll just have to wait for it to lay an egg.
All of these method require the bird to be at least 6-8 weeks.