Like anyone who works with painting, design or color in any form, I occasionally struggle with color; not just with mixing and choosing colors, but with the actual perception of color, the ability to answer the seemingly simple question “What color is that?”
All of my studies of color and color theory have led me to the inexorable conclusion that the single most important rule of color is that the human perception of any color is almost entirely dependent on adjacent or surrounding colors.
This is the basis of Eugene Delacroix’s wonderful quote: “I can paint you the skin of Venus with mud, provided you let me surround it as I will.”
While this principle is visible to the trained eye, both in painting and in life, it is never made more clear than in deliberately created optical illusions, like the e-Chalk color perception illusion I wrote about in this post.
This image shown here is one of the most striking illustrations of this principle I’ve seen.
I came across it in a post by Phil Plait on Bad Astronomy, who indicated the the original is from Akiyoshi Kitaokaâ’s optical illusion website (scroll to the bottom of the page).
Anyone with normal color vision will see a series of green and blue spirals. There would be little chance that a casual observer would suggest that the blue and green might be the same color, and yet they are.
You can see in the first detail image that the “green” spirals are only crossed by bands of orange, and the “blue” spirals are only crossed by bands of magenta.
In the second detail, you can see the Photoshop foreground/background color blocks where I have used the Eyedropper tool to pick one color out of the “green” band, and the other out of the “blue” band.
They are identical RGB values, 0, 255, 150. The same color.
The color is actually a green leaning toward blue. Richard Wiseman used Photoshop to change all of the values except the green and blue bands to black, and you can see a detail of the result in the bottom image. There is also a simplified version of the illusion here.
So the next time you’re looking at a color an think “that’s green” or “that’s blue”, well, maybe it is, maybe it isn’t, depending on the surrounding colors.