Var.: Чёрного ворона не вымоешь добела
Cf: Bad is the wool that cannot be dyed (Am.). Black will take no other hue (Am., Br.). A crow is never /the/ whiter for washing herself oft (often) (Br.). A crow is no whiter for being washed (Am.). Wash a dog, comb a dog: still a dog (Am.). You cannot wash a blackamoor (charcoal) white (Br.). You can't paint the devil white (Br.)Русско-английский словарь пословиц и поговорок. Академик.ру. 2013.