The appearance of a light or object depends on what is around it. In the animation below, the large rectangle has a gradient that should look like it varies smoothly from red at the left to green on the right. The smaller rectangle is uniform (to the extent that your monitor is working as it’s designed). However, when the smaller rectangle is within the larger one, it does not look uniform. If it does ‒ and even moreso if the larger rectangle looks uniform to you, you should have your color vision tested by an optometrist or ophthalmologist. What you should see is that when the smaller rectangle is within the larger one, the left end is slightly greenish, and the right end is slightly reddish.
The Simultaneous Color Contrast Effect
This effect is best seen if you look quickly back and forth at the left and right ends of the smaller rectangle and ask yourself if they look the same. You can stop the animation in different places, particularly when it is deep inside the larger rectangle and again when it is completely outside. Compare the ends of the smaller rectangle under these two conditions. To stop the animation, right click on the image (Windows) or hold down the control key and click (Macintosh) and uncheck “Play” in the menu that comes up. To restart it, just check “Play” again. If you’re really gung ho and want to make sure I’m not playing a trick on you, stop the animation with the small rectangle inside the gradient, get some black construction paper and cut a window into it so that you can cover the background and just see the small rectangle. Notice that when you remove the context that way, the rectangle looks uniform.
If the smaller rectangle has the property “color”, then why does that property change when you see it in a new context? You can say that it is uniformly tan and just looks different inside the gradient, but that statement is purely arbitrary. You could also say that it is reddish at one end and greenish at the other and just looks different when surrounded by a black background.
This page was last edited on August 25, 2004.
© 2004, Mickey P. Rowe