Sasha, dun heifer calf
One can see from this photo of a dun heifer calf maybe why the early Dexter registries listed the color dun as red. I believe that it was in the 1970's the distinction of being two colors, dun and red, was made in the UK. There were dun Dexters in the early and original American Dexter herds and in the 1980's dun was given a separate color distinction in the U.S. registry. Registrations were listed as red/dun since many breeders weren't sure of which. While originally black was the popular Dexter color, later importations increased the number of dun and red Dexters in North America.