If you own an iPad, I recommend you install a marvelous app created by the Exploratorium in San Francisco. (And if you’re ever in San Francisco, I highly recommend you visit this fascinating museum.) The app is free and called Color Uncovered. It’s an interactive book filled with illusions, activities, articles and videos which explores the nature and properties of color.
Here’s a sample of one of its activities.
When is Yellow Yellower than Yellow?
Hold a white piece of paper over the right side of the circle and stare at the X for 30 seconds. After 30 seconds, take away the piece of paper but keep staring at the X.
What’s going on? Wow — the right side looks yellower than the left side. The difference in perceived saturation comes from a phenomenon called adaptation. After staring at the same color for a while, the color-sensitive cone cells in your eyes stop responding as strongly as they did at first. This reduced response becomes obvious when you compare it to a “fresh” view of the same color. Actually, there’s nothing special about yellow. It works with any color.