In other words, this is the visual version of "if a tree falls in the forest...", except that we already defined 'color' as qualia rather than wavelengths, right?
Since you mention it, that's something I should have brought up in one of the Mitchell_Porter consciousness threads: the colors you see are not actually matched up one-to-one with the wavelengths hitting your retina. Rather, the visual system does something like subtracting away the average color.
Meaning, the color that you experience seeing depends on all the colors in the scene, not just the wavelength of the light coming off each specific object.
Some people were talking as if you were getting direct knowledge of (something equivalently expressible as) wavelengths, which is unfortunate, since part of the path to demystifying qualia is understanding this kind of processing.
Today I looked at the above illusion and thought, "Why do I keep thinking A and B are different colors? Obviously, something is wrong with how I am thinking about colors." I am being stupid when my I look at this illusion and I interpret the data in such a way to determine distinct colors. My expectations of reality and the information being transmitted and received are not lining up. If they were, the illusion wouldn't be an illusion.
The number 2 is prime; the number 6 is not. What about the number 1? Prime is defined as a natural number with exactly two divisors. 1 is an illusionary prime if you use a poor definition such as, "Prime is a number that is only divisible by itself and 1." Building on these bad assumptions could result in all sorts of weird results much like dividing by 0 can make it look like 2 = 1. What a tricky illusion!
An optical illusion is only bizarre if you are making a bad assumption about how your visual system is supposed to be working. It is a flaw in the Map, not the Territory. I should stop thinking that the visual system is reporting RGB style colors. It isn't. And, now that I know this, I am suddenly curious about what it is reporting. I have dropped a bad belief and am looking for a replacement. In this case, my visual system is distinguishing between something else entirely. Now that I have the right answer, this optical illusion should become as uninteresting as questioning whether 1 is prime. It should stop being weird, bizarre, and incredible. It merely highlights an obvious reality.
Addendum: This post was edited to fix a few problems and errors. If you are at all interested in more details behind the illusion presented here, there are a handful of excellent comments below.