Which color, along with its dilute version, is sometimes cited as very seldom seen in conformation shows or breeding programs?

Answer

Brown/Chocolate

Some sources point toward the Brown/Chocolate color, or its dilute version, as being exceptionally uncommon in general breeding programs and conformation shows.

Which color, along with its dilute version, is sometimes cited as very seldom seen in conformation shows or breeding programs?
rarityDogcolorbreedgreyhound