They look a little on the light side, but over all, based on pictures alone, don't look too bad. You should not be able to easily feel backs or hips though. What kind of diet are they on?

As for how to breed solid colored black or brown (agouti I assume?) rats... That shouldn't be too difficult. Select the rats with the least amount of white and breed those. Also select black and/or agouti rats and breed only those. Eliminate animals with a lot of white or who are not black or agouti. Since all other colors are recessive, it is just a matter of avoiding those colors in the breeding line. You COULD still end up with other colored rats if the parents are carrier (het), but simply don't breed those animals for future litters.