Colour Harmony

Complementary

Complementary colours are a colour harmony, which uses opposites. Such as Red and Green, or Blue and Orange. 

Analogus

This method uses similar colours, such as shades of Green, and colours close to them. 

Split Complementary

This has colours that are almost opposites, and puts them together. There are many variants of this effect, such as Triadic, Rectangle, etc.

Square

The square uses 2 sets of complementary colours. Such and Red And Green, with Blue and Orange.