PRIMARY COLOURS This definition really depends on what type of medium of color we are using. The colors that are seen when sunlight is split by a prism are sometimes called the spectral colors. These are red, orange, yellow, green, blue, indigo, and violet. These ROYGBIV colors are often reduced to three "red, green, and blue-violet" which are the primary colors for the additive color system (light). The primary colors for the subtractive color system (paint/pigment) are "cyan, magenta and yellow." Notice that "red, yellow and blue" should never be used as the combination for color primaries!
SECONDARY COLOURS Secondary colours result from the mixing of two of the primary colours. Red (magenta) and yellow produce orange, yellow and blue (cyan) produce green while red and blue (cyan) produce violet. For example, if you add more red than yellow, you get a reddish orange, and if you add more yellow than red, you get a yellowish orange.
TERTIARY COLOURS Tertiary colors are browns and grays, containing all three primary colors. They're created by mixing either all three primary colors or a primary and secondary color (secondary colors of course being made from two primaries). By varying the proportions of each primary color, you create the different tertiary colors.
COMPLEMENTARY COLOURS Colours that are opposite one another in the chromatic circle are called complementary. For example, green (resulting from the mixing the primary colours yellow and blue [cyan]) is complementary to red. Orange (a mixture of yellow and red [magenta]) is complementary to blue, while violet (a mixture of blue [cyan] and red [magenta] is complementary to yellow.
HUE This is what we usually mean when we ask "what color is that?" The property of color that we are actually asking about is "hue". For example, when we talk about colors that are red, yellow, green, and blue, we are talking about hue. Different hues are caused by different wavelengths of light.
CHROMA Think about a color's "purity" when describing its "chromaticity" or "CHROMA". This property of color tells us how pure a hue is. That means there is no white, black, or gray present in a color that has high chroma. These colors will appear very vivid and well, ... pure. This concept is related to and often confused with saturation. However, we will continue to use these terms separately because they refer to distinct situations, as explained here.
SATURATION Related to chromatic value, saturation tells us how a color looks under certain lighting conditions. For instance, a room painted a solid color will appear different at night than in daylight. Over the course of the day, although the color is the same, the saturation changes. This property of color can also be called intensity. Be careful not to think about SATURATION in terms of light and dark but rather in terms of pale or weak and pure or strong.
TINTS/TONES/SHADES These terms are often used inappropriately but they describe fairly simple color concepts. The important thing to remember is how the color varies from its original hue. If white is added to a color, the lighter version is called a "tint". If the color is made darker by adding black, the result is called a "shade". And if gray is added, each gradation gives you a different "tone."