Colour Wheels are a tremendous help to those who have difficulty mixing colours.
The wheel shows and explains Primary Colours, Secondary Colours, Tertiary Colours, Complementary Colours, Split-Complementary Colours, Shades Tones and Tints. In fact all colour relationships.

The Pocket Colour Wheel is a smaller version of the larger.

The Watercolour wheel is different, it shows how twelve common colours combine to help artists in mixing colours. It gives an indication of a pure colour wash of each colour as well as the undertone. It also describes the opacity, and staining capabilities of the colours as well as where they are most often used