We expect the universe shortly after the Big Bang to be filled with the quark-gluon plasma (QGP). Now, if I apply my understanding of electric charge to color, then the fact color charge is conserved does not mean the total charge is 0 (if the universe is spatially infinite; let's assume it is). Thus the early-universe QGP could perfectly have an excess of, say, red, as a initial condition from the Big Bang. Since there's no confinement in the QGP, this excess red doesn't seem to cause any problem, naively.
But then the universe cools down, eventually, and the QGP transitions to the confined phase. Where does the excess red go? It doesn't seem that a system in the confined QCD phase can have a net color charge.
If I unpack all my assumptions, it seems at least one of these must be the case:
- The universe is bounded spatially, so that all net charges (electric, color, etc) are 0.
- Due to fundamental reasons (not derivable from QCD?), all net color charges are 0. A universe with net charge is not a valid initial condition for the Big Bang.
- The QGP cannot have a net color charge. The confinement argument doesn't apply here, but another argument does.
- The linked post is wrong and QCD in the confined phase can have a net color charge.
- The QGP will never transition to a confined phase if there's a net color charge.
