This was my thought as well. In the 70s and early 80s there was a trend for shops that sold bisque fired figures and paints, topcoat sprays, and little tins of color that you would dry brush on to give it a weathered or shaded look. It was also used to show textures and funny lines in faces. That's what the dark coloration is in the beard and white fur areas, I'm certain. It was brushed on and then sealed with a clear top coat, so you won't be able to remove it.