Colour Theory

The colour wheel, the basic tool for the combining of colours, s the most common version that holds 12 colours based on the RYB (or artistic) colour model.

There are a number of colour combinations that are called colour harmonies/chords that consist of two or more colours that have a fixed relation to the colour wheel. Some colours can compliment each other when they are the opposite colour on the colour wheel.
Analogous colour scheme is when colours that are next to each other on the colour wheel and usually match well. Triadic uses colours that are evenly spaced on the colour wheel, thus making a triadic harmony. Split-complemetary colour scheme is a variation of the complemetary clour scheme, where one chooses a base colour and uses the two colours adjacent to its complement.
Rectangle colour scheme uses four colours that are arranged in two complementary pairs.
And last, but not least, the square colour scheme, similar to the rectangle, uses colours that are spaced evenly on the colour circle.

The three colours that are exactly opposite each other on the colour wheel: red, yellow and blue.
By mixing two primary colours, there are three different secondary colours: green, orange and purple.
Tertiary colours are made by mixing primary and secondary colours together, and in total, there are six.

As well as primary etc colours, each colour has a cool or vibrant warmth to it. Therefore, the colours can be divided into cool or warm colours. Warm is evidently symbolic for vividness, energy and advances in space; cool colours give the impression of calmness. Black, white and grey are considered to be neutral.

The mixture of black/white/grey with a colour creates tints, shades and tones. Tints are created by adding white to a pure hue/colour; shades are when black is added to a colour and tones are when one adds grey to a colour/hue.