A pocket color wheel is a compact, easy-to-reference and often interactive visual guide to color mixing. It is essentially just a smaller, more convenient version of the large color wheel prominently used in color theory.
Invented by Sir Isaac Newton in 1666, color wheels are based on the primary colors of red, yellow and blue. They typically display the secondary colors green, orange and violet, which are formed by mixing the primary colors, and the tertiary colors such as blue-green and yellow-orange, which are formed by mixing primary and secondary colors together.
A common diameter size for a compact colors wheel is 5 1/8 inches, and these wheels are often made using cardboard. Whereas the term "color wheel" generally refers to a theoretical diagram, a compact version features a movable wheel with slots to display directions for color mixing.