At some point, someone in Hollywood decided that White, thin, cisgender, non-disabled women who otherwise fit the (white, patriarchal, cisgender, etc.) beauty standard could be “ugly” if they have brown hair. Huzzah! Now we can appreciate a compelling storyline without having to endure all of the discomfort that attends watching TV where one of the female characters isn’t white, cisgender, non-disabled–or genuinely ugly.
So in addition to robbing legitimately ugly/nonwhite/disabled/trans/etc. women of representation, I think the “dark hair/eyes = pretend she’s ugly” formulation is starting to serve as an excuse for white women (who are, by virtue of–like–being white given an automatic pass on the white beauty standard) with brown hair to claim that they are somehow more oppressed than their blond/redhead counterparts. This is super appropriative of nonwhite women’s experiences, especially when you consider the fact that the canon of “conventionally beautiful” actresses are proportionately brunette–but almost all white.
On the other hand, women of color are generally praised for having lighter skin/features for the sole reason that those features are considered “whiter.” But of course, there is no pinnacle of whiteness, whereby nordic/blond women are “whiter” than other white people. And so there is no punishment for being a white person (or a passing-as-white person) who would otherwise fail the impossible test of beauty designed strictly for women of color.