The Phenomenon of Simultaneous Contrast
OK, look at the difference here. See how the letters in the above title appear much brighter than the same colored words you are reading right now? Because of the strong contrast of the dark background, the bright letters above almost glow. This is one of the tools that Amy Lindenberger uses when teaching her workshop "Colored Pencil on Colored Paper", which is also the title of her new book. Want to bring attention to a certain area in your drawing? Use the concept of Simultaneous Contrast.