Which 牛 breeds come in 纯色?

Club breed standards describe 纯色 for the 娟姗牛和瑞士褐牛.

牛 pattern

纯色

One color all over with no pattern or white: self in rabbits, cavies, rats and canaries; a tongue or hoof of one even color.

5 牛 breeds list 纯色. It is in a club standard for 2 breeds.

Breed	PDCA	BROWN SWISS USA
娟姗牛	符合标准 (“with or without white markings”)	No ruling
瑞士褐牛	符合标准 (“solid brown”)	符合标准 (“solid Brown”)

How 纯色 can appear or change over an animal's life.