  The brightnesses of supernovae are commonly understood to indicate that
cosmological expansion is accelerating due to dark energy. However the entire
discussion presumes a perfectly transparent universe because no effects of
reddening associated with the interstellar extinction law are seen. We note
that with two kinds of dark matter (baryonic and non-baryonic) strongly
dominating the known mass of the universe, it is seriously premature to assume
that these dark matter components have not reduced the transmission of the
universe for cosmological sources.
  We show that the long-known $Lyman-\alpha$ clouds, if nucleated by the
population of baryonic dark matter primordial planetoids indicated by quasar
microlensing, would act as spherical lenses and achromatically fade
cosmologically distant sources. We attempt to estimate the amount of this
cosmological fading, but ultimately the calculation is limited by lack of a
satisfactory model for the tenuous outer parts of a primordial planetoid. We
also consider the effects of such cosmological fading on the light of quasars.
