Two parent mice with black fur have offspring with white hair.
Since both are heterozygous, that means they both have a dominant and recessive allele, but since they have a dominant, that trait is displayed. Since both also have a recessive allele, there is a possibility that they can have offspring with a recessive trait.
In other words, if you have 2 heterozygous parents that show a dominant allele, offspring that display the recessive allele is possible.
Hope this helps :)
