what is the best way to improve the yellow of tan mice bellies? should i breed a yellow to a black tan and that will help the yellow pigment? or should i breed two black tans and pick the best yellow pigmented pups from their litters?
Homogeneous animals typically have better pigment then heterozygous ones.
There really aren't any shortcuts you can take with tan.
Yellow is dominant over black so it won't add anything, most yellows also have very pale bellies which is not the goal here.
Breed for homogeneous only, select the offspring that have the better colour distribution each time.
Try to breed away from faults like black showing theu the tan on the chest *(think moon bear)
Early in the line progress might seem very slow but after a few generations you will notice the improvements.
Try to keep the line as pure as you can.
Blue is a recessive that will wash out the tan belly.
Chocolate can degrade the quality of the black .
And pink eye dilute is just not something you want in there anyway.