Of course I do have synesthesia, and I’m not colorblind. Bully for me! But the fact that I can actually see the pattern here is rather lucky: it just so happens that all of the numbers Randall chose to include in the foreground have warm colors, and most of the others are cool, so the background literally recedes for me.
But wait. What’s that he said about colorblindness? The most common forms of colorblindness are protanopia and deuteranopia, where people are missing either the red or the green light-sensing cones. Both have trouble distinguishing reds from greens and browns. Which just happen to be the colors inside the numbers for me. And as you can see below (um, if you’re not colorblind, that is) the big numeral 4 contains red 2′s, and the big 2 contains brown 9′s. So if you actually used my synesthetic picture of this thing as a colorblindness test, it might actually kinda sorta work!
I’ve never met Randall Munroe, but I’m starting to wonder. Randall, if you’re reading this, fess up. Did you crib my colors?