I picked the following quote off the Genetics Forum at Classroom at the Coop. What it means is that for chicks that are birchen or brown red (ER at the e locus and having black down), there is a way to tell the gender at hatch with a fair amount of certainty. About 71.7 % of females will have white or pink toes/feet, while males will have uniformly pigmented shanks and toes. Not nearly 100% accurate, but it is another tool for the toolbox for us brown red breeders. (Anybody want to buy some chicks? - most of them will be males.) The quote follows:
"Sexually dichromatic variation in shank melanization, similar to that described in Barred Plymouth Rock chicks, was observed in the absence of sex-linked barring (B) in black-down birchen (ER) chicks. The shanks of male chicks are uniformly pigmented. The female chicks have more darkly pigmented shanks, and pigmentation is frequently restricted in the distal portion of the shank and toes. Among chicks definitely demonstrating the male or female phenotype, 80.2% were accurately sexed. An intermediate shank type was observed in 35.1% of the total number of chicks, and these were sexed with 55.9% accuracy. A total of 71.7% of the birchen (ER) chicks were accurately sexed on the basis of shank color alone. This accuracy in sexing is similar to that observed in Barred Plymouth Rock chicks."
Although no study on this has been reported, I see no reason why the same tool could not be used on blacks and blues that are based on ER - and maybe lavenders too. Anybody raising those varieties care to do a study and let us know?