Due to how quantum chromodynamics works, free particles should be white (or colorless). That is, their constituent particles (in this case, quarks and gluons) have a “color” (red, green, blue for quarks, and their inverses for antiquarks) and they must come together in such a way to cancel out in any free particle like a proton.

So here the 2 red 1 blue means 2 up 1 down, right? And the QCD color is different from this, and so it's misleading?

Oh, is that what the color represents? I thought it must have been color charge…