QCD and confinement specify that hadrons must be color-neutral. My understanding is that this means you can have mesons (quark + antiquark) or baryons with 3 quarks, one of each color: Red+green+blue=neutral. In a meson, does the color of the quark and antiquark matter? Must a red quark be paired with a red antiquark; or does the color change constantly due to the exchange of gluons which also carry color charg?
The color charges are paired (color with anticolor), but there's no gauge invariant meaning to the identification of the color (RGB). And due to QM, the quark states are a superposition over all the colors (and antiquarks over the anticolors). The wikipedia page is pretty clear: http://en.wikipedia.org/wiki/Color_charge. As it notes, you also can't distinguish a color from a certain superposition of the two non-complementary anticolors (e.g., R from a combination of anti-G + anti-B).