Mary Gartside was an English watercolor painter and color theorist. Not much is known about her personal life. She probably grew up around Manchester. She taught painting in watercolor, probably in London, and exhibited her flower and botanical drawings at the Royal Academy in 1781 and at a number of other art societies until 1808. A number of her letters survive in the records of the Associated Artists in Water-Colours, where she exhibited in 1808. She published three books between 1805 and 1808, all dealing with color theory and its application in the art of watercolor painting: An Essay on Light and Shade (1805), Ornamental Groups, Descriptive of Flowers, Birds, Shells, Fruit, Insects etc. (1808); and a second edition of the first with a new title, An Essay on a New Theory of Color, also published in 1808. Until well into the 20th century, she was the only woman known to have published a theory of color. Her work has recently been discussed by art scholars. In 2013, a rare copy of An Essay on Light and Shade was included in the exhibition "Regency Colour and Beyond, 1785-1850" at the Royal Pavilion in Brighton.