Why do we need a color filter to create the correct effect?
Apparently in Krita, instead of "Color Burn" (as that doesn't exist) the filter you use to properly mix the colors is "Screen".
Anyway, I find it interesting that the way the colors mix in digital doesn't work correctly unless you use one of these filters... Why is that, exactly? Most monitors and paint programs use RGB by default, so when we mix them normally I would think we should be getting the same results as shown on the modern color wheel. So why, instead, do they turn out weird? Why do we need to use a special color filter, even when the canvas is set to use RGB?
Granted, I say this - I did a little bit of testing and I realize that when you mix opaque red and green at 50% opacity using a Screen filter, it turns out as a light red rather than grey. This is for the same reason as it turns white when both of these colors are fully opaque, as like you said the RGB colors on the screen are additive. But then you also said that the modern wheel is based on the fact that the complimentary colors turn grey when mixed together at 100% and 50% capacities, so... what the heck? The rest of the modern color wheel doesn't work on monitors when you mix them normally, so why would the color wheel be based on them turning grey when they're mixed normally? Or is it actually that they're based on them turning white instead, and the grey is something of a coincidence?
Also why do ink and monitors share a color spectrum? What is it about ink that makes it blend differently from paint? Do different types of paint all blend into their own unique colors, or is this a property specific to ink?