I only used the four colors and used erasing every other row on the top layer to make the illusion of more colors but ONLY FOUR APPEAR!
Peacock feathers down in a limited palette of grey, chartreuse, robins egg blue and butter yellow. I only used the four colors and used erasing every other row on the top layer to make the illusion of more colors but ONLY FOUR APPEAR! Proof shown here: http://www.flickr.com/photos/psarah/8178052228/