Albedo was a term given by alchemists to "whiteness". It was one of the four major stages of the "alchemical opus". Following the harrowing, chaotic nigredo, it is necessary for purification provided by the albedo which is literally referred to as ablutio; the washing away of impurities by aqua vitae.
The image of the card also reflects the primary colors of light (red, green, blue), along with the colors obtained by mixing either of these colors (red + blue → magenta, green + blue → cyan, red + green → yellow). White is obtained when all three primary colors of light are mixed.