"Circus Sideshow" by Georges Seurat 1887-1888

This oil on canvas is a great example of the optical effects of color.  The colors seem to change depending on the degree to which the figure at the right is enlarged.  Our eyes can simulate the effect of mixing colors, called optical mixing.  It happens when two colors are placed next to each other and our eyes combine them as if they are actually mixed.  Seurat uses dots of color placed next to each other and the dots seem to merge into their combined color.