The six-year-old had to have brought it up, because I can't imagine how I would have. But the argument flared so fast I don't really remember how it started. A is red, he was saying, and B is blue.
Blue? What's C then? C is blue.
C is NOT BLUE. How can C be blue?
This was serious. I started drawing an alphabet in the colors that made sense to me, and he started grabbing for the crayons. Stop! You're wrong! He was riled up. I'm correcting you!
The content of low-grade synesthesia ought to be the most subjective thing possible. It's entirely in your own head. Yet there are certain generalizable truths about arbitrary color-letter association. The letter A really does register as red, according to "The Colors of the Alphabet: Naturally-Biased Associations Between Shape and Color," a 2011 paper published in the American Psychological Association's Journal of Experimental Psychology: Human Perception and Performance.
The study's authors, Ferrinne Spector and Daphne Maurer, put subjects of various ages through forced-choice testing between colored boxes. Besides the A, other reported points of agreement in the literature, some apparently influenced by language and others based on preverbal shape-associations, include: B = blue, C = yellow, G = green, I = white, O = white, X = black, Y = yellow, Z = black. (Some of these are so obviously erroneous I don't even know where to begin.)
And the ones that are not universal still feel like they ought to be. Even if your own flesh and blood disputes them. The sight of a D that's not green seems wrong, on some fundamental level. Unless you think D is yellow-orange, which, huh? But there it is.
So there's one young person's alphabet, up top. (As the Q suggests, he also has opinions about letterforms. And the tip broke off the crayon he used for the W.) Below is the alternative that set him off (though really, I think the letter I is white; contrast is less of a problem when you're rendering images in your brain).
We agree on almost nothing—and if you've got color-letter opinions of your own, we're both surely wrong. Put yours into the comments below.