  We propose and show that the dependence of the internal face-on dust
absorption upon B-band luminosity reported by Wang & Heckman (1996) for a
sample of late-type galaxies may explain the empirical color-magnitude and
color Tully-Fisher relations of disk galaxies. Thus, in order to explain these
relations, it is not necessary to evoke star formation and gas infall
efficiencies dependent on the mass of the galaxy system. After applying the
Wang & Heckman's luminosity-dependent extinction to hierarchical inside-out
galaxy formation and evolution models where the star formation and gas infall
efficiencies do not significantly depend on mass, we succesfully predict the
observed Tully-Fisher relations in the H and B bands as well as the
color-magnitude relation.
