In the Natural System of Colours (between 1769 and 1776) he examined the work of Isaac Newton and tried to reveal the multitude of colours which can be created from three basic ones. Natural System of of Colours was published again in 1811, this time edited by Thomas Martyn and dedicated to the second President of the Royal Academy, Benjamin West. As a naturalist, Harris wished to understand the relationships between the colours, and how they are coded, and his book attempted to explain the principles, "materially, or by the painters art", by which further colours can be produced from red, yellow and blue. Harris showed what is now known as the subtractive mixing of colours, with his most important observation showing that black will be formed through the superimposition of the three basic colours.
Moses Harris' 'colour wheel' showning how a multitude of colours could be made from just three.