Andrea of Majna-menti Mákvirág Kuvasz Kennel in Hungary shares this photo of her Coco showing the Kuvasz's distinctive dark gray skin.
“The colour of the skin under the hair is also slate grey, best seen on the belly, where the hair is less thick than on the rest of the body.”
From: Pál Sárkány and Imre Ócsag, Hungarian Dog Breeds, Budapest, Hungary: Corvina Kiadó, 1977, 2nd ed. 1986, p. 103.