Complement

Complement 1 a : something that fills up, completes, or makes perfect b : the quantity, number, or assortment required to make a thing complete  


In Betty Edwards, A Course in Mastering the art of mixing colors, she states, " In this book, I am following Goethe's thought that the response of delight elicited by certain color harmonies may be linked to a phenomenon called "after-images," which suggests that the human brain longs for balanced relationships across  the three attributes of color.