Is this someone who breeds for fancy pets or show, or someone who breeds rodents to sell/breeds feeders?

Feeder breeders are more likely to be careful about having rats that give large healthy litters of fast growing babies. Pet/show breeders are more careful about conformation and color.

Both will be healthy rats if they are a quality breeder, but know the particulars will help you know what to expect.

When you are building the colony, don't be afraid to cull undesirable traits.