This is the first of the “visual deceptions” we are studying in Dick Nelson’s “Interaction of color” class. Many of the principles are easiest to recognize and learn from in shades of gray (values), before trying them in color.
I chose my values from the array I created for the last post.
Here is a proof that they are the same:
This one is quite interesting. If you look at the horizontal bar, doesn’t it look as if it changes color right at the boundary between light and dark?
But Dick says, “If you can push it, why not SHOVE it?” Meaning, really emphasize the effect. To do that, you have to recognize what causes the illusion, and what variables you can manipulate to heighten it. In this case, making the ground values as different as possible from each other is what does the trick. This is what he terms “exploitation”.
Here, if asked to order these values from lightest to darkest, I would say white, the right gray strip, the left gray strip, then black. But in reality, both gray strips are the same middle gray.
What are the principles involved in this illusion? The figure color must be related to both ground colors, in other words, it is a child of the two parents. The ground colors should differ from each other in both hue and value. (Here, they differ only in value. I will explore this illusion in hue, or color, in a later post.)
So what’s the point? The point is, a color looks different depending on its background. So don’t use one color on two different backgrounds and expect the viewer to “read” it as the same – they won’t.