Data are presented on the genetics of the plumage color of the Villafranquina, a breed of Spanish chicken representing a black-tailed red type of the columbian restriction pattern. Crosses between Villafranquina females, which show a large amount of secondary pattern, and Brown and Buttercup tester males suggested that this breed carries the brown allele (eb) at the E-locus. This allele is modified by the dark-brown columbian-like gene (Db), resulting in the plumage pattern characteristic of the breed. The degree of expression of Db varies markedly depending on other key genes present. This gene acted as an incomplete dominant when crossed to brown (eb) and buttercup (ebc) tester lines. However, in the presence of the birchen (ER) gene, Db was recessive in females but dominant in males, suggesting sex-influenced inheritance. Silver (S) does not alter the brown down of Db-modified ER, although it does express itself readily on a brown (eb) background. Variability in the expression of Db in both F1 and F2 populations suggests that it sometimes interacts with not yet identified modifying genes.