It threw me for a while, too, because I was taught "red yellow blue" for two decades, and I'm a computer-ey person so RGB kind of works in my head. I rejected CMY, because it always looks dumpy on a computer screen, which is where I do a lot of my work.

Then I started working with paint and real-world colour, and red + blue does indeed make the most unsatisfying crap purple. A nice, clean, solid purple is my absolute favorite colour, and this red+blue travesty was unacceptable, so I put on my research hat.

Then I bought CMY paint, and lo-and-behold real purple happened. And a bunch of other nice clean colours.

Then I got really really into painting, and couldn't be bothered to try to accurately reproduce the exactly perfectly matched colours every time, so I just started buying paints that only have one pigment that is one specific colour in it … because:

Theoretically, CMY are primaries, but they have to be made out of real world materials, and sometimes those vary by manufacturer. It's usually Quinacridone magenta & Pthalocyanine (cyan), but there are a load of yellows out there with varying levels of toxic elements to them. I try to find PY47 (Lead Titanate) which I thought was the yelloweyist yellow I could find that had the lowest toxicity, but I just looked up, and I was wrong; it's extremely toxic. Good thing I rarely use yellow - and that I don't eat paint, lol.

I now have maybe ten or so single pigment colours so I can always know what I'm getting. And it's never poopy maroon! If you ever need a good purple, Dioxizine purple is your gal. But get some titanium white too, because diox purple is almost black if you don't add a bit of white. Computer screens can't come anywhere properly reproducing it, but trust me, it's pretty. (diox purple is sometimes called Carbazole Violet. Same thing).

Yes, I'm a nerd.