Okay, so both of my slate gray are males (at least one of those was my only one crowing so far), my black & white is a female. I stink at getting pictures of these scared little boogers, so how can I tell on my one that is light red all over? Most of it's feathers are the same color as the other two's vent feathers.
Sometimes the silvers (slate grey) won't have the colored vent feathers either, but most of them do. If your black and white is a tuxedo, that falls under the 'white' category since the belly feathers are white.