Red and green are opposites! Just, in pigments rather than actual light colors, or dyes. This is a distinction that is rarely taught in the US! Most or us only have "art" classes until age 10, if ever, and most of them will only ever use crayons, fingerpaints, etc. All of which are pigment based, not dye. So US kids learn Red-Yellow-Blue (a color system almost unique to painting) instead of CMYK (the color system for dyes, light) or RGB (for limited light, popularly electronics).
This is also why US under-10s are so INSANELY destructive to markers; way moreso than kids overseas. Markers ARE dye based, so all the colors "come out wrong" and then the kid gets pissed. Which I can't wholly blame them for. They're a kid, and they were not just told but SHOWN that mixing RYB makes black, and yet now it's making Horrible Greenish Brown instead.
I hypothesize that this is also why US students at all ages are almost morally opposed to the existence of highlighter markers.
Anyway, it all comes back to a refusal to teach in US schools, at the end of the day.
The "destruction with markers" thing has started spreading, unfortunately, I've heard tell from my relatives back in Europe that kids have gotten more aggressive with their coloring stuff. Though whether this is a factor of worsening color education or worsening treatment of kids, I am not sure.
I have seen some older texts talking about the red-yellow-blue color system where the colors very much look like CMY, which I thought was absolutely FASCINATING. Did the colors fade? Or did the definitions of the colors change?
[long rant about Anglophone definitions of "blue" being indigo omitted because it's too rainy outside for me to be a grumpy Eastern European on main]
Most people I know, both here in the States and back there in Europe, haven't had much art education past the age of ten or eleven (elementary school, where I grew up). My high school has two semesters of art as a graduation requirement, but it was a joke. The smart kids took AP art history, which from what I've heard had less actual history and more rote memorization of five hundred paintings. All the other classes were basically "goof off" ones.
So the "lies to children" form of art education basically becomes the It Is Known of adult art knowledge, and capitalism means that only people who want to Do Art For Money have any motivation/time to do any actual art and learn about it.
(Seriously, almost every time I mention that I do art of any form, people ask if I have like an Etsy store. No?!?! I don't?!?! I have a full time job, and I do art to RELAX and NOT THINK ABOUT the fact that our gas chromatography machine broke AGAIN, who the fuck keeps leaving the lamp in that thing on, we have SIGNS and everything - can you tell I'm posting this while not paying attention to work?)