  The rate of type Ia supernovae (SNe Ia) in a galaxy depends not only on
stellar mass, but also on star formation history. Here we show that two simple
observational quantities ($g-r$ or $u-r$ host galaxy color, and $r$-band
luminosity), coupled with an assumed delay time distribution (the rate of SNe
Ia as a function of time for an instantaneous burst of star formation), are
sufficient to accurately determine a galaxy's SN Ia rate, with very little
sensitivity to the precise details of the star formation history. Using this
result, we compare observed and predicted color distributions of SN Ia hosts
for the MENeaCS cluster supernova survey, and for the SDSS Stripe 82 supernova
survey. The observations are consistent with a continuous delay time
distribution (DTD), without any cutoff. For old progenitor systems the
power-law slope for the DTD is found to be $-1.50 ^{+0.19} _{-0.15}$. This
result favours the double degenerate scenario for SN Ia, though other
interpretations are possible. We find that the late-time slopes of the delay
time distribution are different at the 1$\sigma$ level for low and high stretch
supernova, which suggest a single degenerate scenario for the latter. However,
due to ambiguity in the current models' DTD predictions, single degenerate
progenitors can neither be confirmed as causing high stretch supernovae nor
ruled out from contributing to the overall sample.
