If your whites are the same kind of white (dom or rec), they should breed true. Since you're not getting any white, they must be diferent. Get another bird, one that is known to throw white, and breed it to one of yours. If that doesn't work, get one of the opposite gender and breed it to your other one. You'd think white would be easier, right?
For chocolate, if you are only getting choc females, it's your male who carries choc. If all your females are choc, he probably carries two coppies of the gene. If you're getting chocolate in both genders, both whites carry choc!