A gray goat (Ww) expresses incomplete dominance.
If Mendel were given black mouse & a white mouse & asked what their offspring would look like, he would've said that a certain percent would be black & the others would be white. He would never have even considered that a white mouse & a black mouse could produce a GREY mouse! For Mendel, the phenotype of the offspring from parents with different phenotypes always resembled the phenotype of at least one of the parents. In other words, Mendel was unaware of the phenomenon of INCOMPLETE DOMINANCE.
I remember Incomplete Dominance in the form of an example like so:
RED Flower x WHITE Flower ---> PINK Flower