To ensure your background colors will still look good when the painting is finished, its best to paint the background at the same time you paint the subject. Waiting until the subject is complete to fill in the background often ruins the painting because we tend to judge colors by how they appear next to other colors. If you paint the model first, youre likely to choose colors that look good alongside the color of the canvas or paper as opposed to the colors of your background.
I also recommend using some of the colors from the background in your model and visa versa. When you share colors between the figure and the background, you weave the painting together so all the parts are cohesive. If you fail to do this, the figure may sit on the background as if it were cut out of another piece of paper and glued onto the surface of the painting.
Beth Derringer-Keith is an assistant editor for The Artist’s Magazine.