I realized that I didn't get to the main point of my thought yesterday.
I understand that when people pull out the "I can't believe people could hate other people just because of the color of their skin" nonsense, they don't usually mean it literally. I'm sure there's some kind of literary term like synecdoche or apostrophe for what they're doing--trying to distill the concept to a very simple, clearly ridiculous form to belittle it as much as possible (reductio ad absurdum, maybe, but that doesn't seem quite right).
But the problem with that technique is that racism, though ridiculous, is not simple. It's a hell of a lot more complicated than superficially similar phenomena like misogyny and homophobia, for example*. And when we turn an oversimplified (not to mention inaccurate) description of it into the ritual utterance that the "color of their skin" statement has become, we run the risk of dumbing ourselves down and convincing ourselves that the simple version is accurate enough.
If you asked someone who made a "color of their skin" comment if they really thought that was all there was to racism, chances are they probably would say no (although I won't say this with certainty; probably some small but not insignificant portion would say yes). But if pressed to elaborate, how many could? In fact, I'd almost go so far as to say that when people say "I don't understand how anyone could hate someone just because of the color of their skin", it's shorthand for "I don't understand anything about racism--its history, its present expressions, its real-world impacts, nothing. But that's OK, because I myself don't actively hate Black people, so I'm not contributing and don't need to educate myself about it. Right?"
As a side note, I feel that I should point out that yes, I am aware that Martin Luther King, Jr., is often quoted along these same lines. It was one of the things he dreamt about--"a dream of a land where men will not argue that the color of a man's skin determines the content of his character"**. And I say that that one bit should not be quoted as often as it is, or at least not on its own. What gives it its power (aside from its brevity and its alliteration, which incidentally combine to explain why King limited this particular statement to skin color) is its inclusion in a long list of King's dreams--a list that includes equality for Jews and Italians, and which, on either side of this very familiar quote, hammers home the class-based critique of America that was King's primary concern, and which most of us are now unaware of. Because King knew that class is at the heart of American racism, that all these other things that people focus on--the color of people's skin, the more complicated matter of genealogy--are actually stand-ins for class, and signify the extent to which America's poor, and especially America's poor whites, have been successfully trained to blame everyone but the wealthy classes who are actually responsible for their own poverty.
(And it turns out, as is so often the case, that my "side note" ended up enabling me to finally get at my main point.)
*If someone actually reads this and actually comments and wants elaboration on that, I hopefully will be able to get around to providing it later. Otherwise I'm considering it self-evident.
**And by the way, how often do people quote the next bit? "(A) dream of a nation where all our gifts and resources are held not for ourselves alone, but as instruments of service for the rest of humanity." Or the part right before it? "A dream of equality of opportunity, of privilege and property widely distributed; a dream of a land where men will not take necessities from the many to give luxuries to the few." If you're wondering why the man got shot, that's it right there***.
***That's another thing I can elaborate on if pressed.