  In the present paper, the dual symmetries of dense quark matter phase diagram
found in some massless three- and two-color NJL models in the mean field
approximation have been shown to exist at a more fundamental level as a dual
transformations of fields and chemical potentials leaving the Lagrangian
invariant. As a result, the corresponding dual symmetries of the full phase
diagram can be shown without any approximation. And it has been shown not only
in the NJL models, but also in framework of two- and three-color massless QCD
itself. This is quite interesting, since one might say that it is not very
common to show something completely non-perturbatively in QCD.
