Isabelline (isabella), brownish-whitish-yellow colour, like café au lait, is said to have gotten its name from Spanish Princess Isabella Clara Eugenia, daughter of King Philip II of Spain and sovereign of the Spanish Netherlands. She vowed that she would not change her shirt until her husband, Archduke Albert VII of Austria, had conquered Ostend, which he started to besiege in 1601. Since this siege lasted three years, the legend could not be in doubt as far as the colour is concerned. Isabell-coloured horses are called isabelline or palomino.
Source: Meyers Großes Konversations-Lexikon, 6. Auflage 1905–1909