On what Dr Little called the E locus, E allows the expression of eumelanin (black pigment) in the hair. Homozygous ee prevents that expression, even if there are genes for black at other loci . Hence Little used the term “epistatic” foe the ee (red/yellow) — it can affect the expression of genes not at the E/e locus. No doubt more recent researchers have a more detailed explanation, but that works for most purposes.
This explains why Golden retrievers can carry the genes for color patterns such as black-and-tan and sable that then can be expressed in their offspring that inherit E from the other parent.