Hue refers to the basic colour, such as red, blue, yellow, etc. BS 4800 is the British Standard for colour coordination. It contains 100 colours divided into categories based on hue, greyness, and tone. Colour schemes can be warm/advancing using red, yellow and orange hues, or cool/receding using blue and green hues. Monochromatic schemes use tints and shades of a single hue. Harmonious schemes use analogous or related hues. Complementary schemes pair hues directly opposite each other on the colour wheel.