BRST invariance supplies a sufficient condition for the observability
of fields. We show that there is a global obstruction to the observabi
lity of quarks and gluons and argue that they will not become observab
les at finite temperature. We give expressions for quarks and gluons t
hat are, however, perturbatively BRST invariant, and hence locally obs
ervable, up to order g2 and g respectively.