A study of the color diversity around maximum light in Type Ia
  supernovae
  From a sample of 12 well-observed Type Ia supernovae, we find clear evidence
of correlations between early phase (U-B), (V-R), and (V-I) colors and the
velocity shifts of the [Fe II] \lambda 7155 and [Ni II] \lambda 7378 nebular
lines measured from late-phase spectra. As these lines are thought to trace the
ashes of the initial deflagration process, our findings provide additional
support to the new paradigm of off-center explosions in Type Ia supernovae, and
we interpret these correlations as viewing angle effects in the observed
colors. We also show that the nebular velocity shifts are related to the
strength and width of the Ca II H&K and IR-triplet lines near-maximum light.
The evidence presented here implies that the viewing angle must be taken into
account when deriving extinction values and distances in future cosmological
studies based on Type Ia supernovae.
