As legend has it, Isabella, the daughter of Phillip II of Spain, pledged not to change her linen (underwear) until the fortress was taken during the Siege of Ostend in the Eighty Years’ War and the Anglo–Spanish War. The siege lasted three years, and after all that time, Isabella’s linen had turned a distinct taupe/brown mouse color. Because of her pledge, the coat color of certain breeds (and not just dogs, but horses, bears, and birds, as well) came to be called “Isabellan,” or Isabella.
As much as we like this theory, at least one source (the Oxford English Dictionary) has discounted it because the word was in use before the siege had begun. Some etymologists have suggested that the word began as a corruption of the word, “zibellino” which was a sable pelt similar in color. Others maintain that the Arabic word for lion, izah, is the origin, indicating an intended original meaning close to “lion-colored.”
Image: Weimaraner by Justine Osborne