Different schools teach different things; many don’t introduce colour theory at all. And it’s an odd thing, but most people don’t know intuitively how colours combine or invert. Of course, as a synesthete and maybe a tetrachromat, I’m not really statistically relevant to this discussion. ;)

Not only that, but I'm pretty sure everyone was taught that the opposite of blue was orange and the opposite of purple as yellow.

Same. I know this, but only from looking at negatives.