I think it's that same "wild type" allele we were talking about with someone else's calf. Pops up here and there (and kinda ugly in my opinion unfortunately).
From Sheila Schmutz's page:
"However E+ appears to act as a "neutral" allele in most breeds and we think ED /E+ cattle are typically black and E+/e cattle are typically red. E+/E+ cattle can be almost any color since other genes,such as the Agouti gene, take over in dictating what pigments are produced. "
So basically, there are three alleles that you can get at the gene. In most beef breeds, I think the plain old red and black are the most common (Breeds like Brown Swiss and Jersey would be where wild type predominates). So if the bull and cow both have and pass on this neutral allele, then you can get these weird colours. Like brindle, and brown. Think of it as recessive like TH, but with two differnt things that can be dominant over it, either red or black.