Pairs of colours which, when additively mixed, combine to produce white light. Examples are red + cyan, green + magenta, and yellow + blue.
Two hues directly opposite one another on a colour wheel which, when mixed together in proper conditions, produce a neutral grey.
Two hues directly opposite one another on the colour wheel. The complement of each primary can be produced by mixing the two other primaries. When mixed together they produce greys and browns (tertiary colours.)