Allowed colors are red, sesame (a red with recessive black gene that manifests itself as a sooty overlay), and black and tan. (texaswestveterinarian.com)
Although, recent studies have shown that even with the dominant black gene present the brindle still appears. (dogdojo.org)
The brindle gene is a recessive part of the K series / K Locus of genes which is dominantly black, recessive brindle and recessive non-solid black genes. (dogdojo.org)