The colour wheel helps us define the relationships among the various colours.
The chromatic spectrum visible to the human eye is wrapped in a circle shape, that lets us perceive the possible derivations and conjugations and the various harmonic relationships.
In nature, it is from primary colours like the yellow, blue and red that all colours are derived from.
From the combination of these, we obtain the secondary colours.
From the combination of primary colours with secondary colours, we obtain tertiary colours.
These are the colours that occupy opposite positions in the colour wheel.