In lecture today we were reviewing the QCD lagrangian, and discussing hadronic wavefunctions. My lecturer said that QCD alone allows for states of colored hadrons, however because we do not see anything like this in nature, we then also simply demand that every hadronic wavefunction be an $SU(3)$ colour singlet. For the same reason (we don't observe long range strong interactions) we deny the existance of the singlet gluon.
Is this QCD + this phenomenological-singlet-heuristic approach still the best way of understanding confinement, or is there a better way?