Your current "mutt" offspring are all positive hets for both types of albino (are you sure one parent or the other isn't Rainwater as opposed to Tremper/Bell? ).
When those offspring cross, you get a menagerie of possibilities.
Each offspring has a 25% chance to be one visible (homozygous) albino type. Each has a 25% chance to be the other albino type, too. Each offspring simultaneously has a chance of being het for either albino type. Meaning, you could wind up with a visible albino of one type that's also het for the other albino type. The offspring can't be visible albinos of both types.
Most breeders with project goals don't want double albino hets, because breeding subsequent generations will give uncertainty as to which kind of albino (i.e., the one a given project calls for) you're hatching. That can be a big setback to a bloodline.
It's important to note that, for the sake of pet animals, this couldn't matter less. If anything, here that uncertainty can be looked upon as a nice surprise. The important thing is simply to not misrepresent the genetic possibilities of what's being sold.