Mildew is a form of fungus. It is distinguished from its closely related counterpart, mold (British English: mould), largely by its color: molds appear in shades of black, blue, red, and green, whereas mildew is white. It appears as a thin, superficial growth consisting of minute hyphae (fungal filaments) produced especially on living plants or organic matter such as wood, paper or leather. Both mold and mildew produce distinct offensive odors, and both have been identified as the cause of certain human ailments.