It is generally thought that Ewald Hering (19th century), or possibly Leonardo da Vinci (16th century), first recognized the concept of four unique hues (blue, green, yellow, red). However, in the Alhambra palaces, Granada, Spain, in a room roped off from tourist traffic, is a stained glass window featuring the four unique hues, built about 1370. (C) 2006 Wiley Periodicals, Inc.