of light, yellow is also associated with knowledge and wisdom. In English and many other languages, "brilliant" and "bright" mean intelligent. In Islam, the yellow color of gold symbolizes wisdom. In medieval European symbolism, red symbolized passion, blue symbolized the spiritual, and yellow symbolized reason. In many European universities, yellow gowns and caps are worn by members of the faculty of physical and natural sciences, as yellow is the color of reason and research. Gold and blond In ancient Greece and Rome, the gods were often depicted with yellow, or blonde hair, which was described in literature as 'golden'. The color yellow was associated with the sun gods Helios and Apollo. It was fashionable in ancient Greece for men and women to dye their hair yellow, or to spend time in the sun to bleach it. In ancient Rome, prostitutes were required to bleach their hair, to be easily identified, but it also became a fashionable hair color for aristocratic women, influenced by the exotic blonde hair of many of the newly conquered slaves from Gaul, Britain, and Germany. However, in medieval Europe and later, the word yellow often had negative connotations; associated with betrayal, so yellow hair was more poetically called 'blond,' 'light', 'fair,' or most often "golden". Visibility and caution Yellow is the most visible color from a distance, so it is often used for objects that need to be seen, such as fire engines, road maintenance equipment, school buses and taxicabs. It is also often used for warning signs, since yellow traditionally signals caution, rather than danger. Safety yellow is often used for safety and accident prevention information. A yellow light on a traffic signal means slow down, but not stop. The Occupational Safety and Health Administration (OSHA) uses Pantone 116 (a yellow hue) as their standard color implying "general warning", while the Federal Highway Administration similarly uses yellow to communicate warning or caution on highway signage. A yellow penalty card in a soccer match means warning, but not expulsion. Optimism and pleasure Yellow is the color most associated with optimism and pleasure; it is a color designed to attract attention, and is used for amusement. Yellow dresses in fashion are rare, but always associated with gaiety and celebration. Mayan and Italian The ancient Maya associated the color yellow with the direction South. The Maya glyph for "yellow" (k'an) also means "precious" or "ripe". "Giallo", in Italian,