1 Introduction -- 2 Data -- 3 Methods -- 4 Results and Discussion -- 5 Conclusions.

This thesis presents a novel analysis of a photometric observational feature of Type Ia Supernovae (SNe Ia), the most precise distance indicators available for cosmological studies. While SNe Ia are crucial for understanding modern cosmology, there are systematic uncertainties associated with them that prevent use to their full potential. It is therefore vital that sources of systematic error in SN Ia standardization are better understood. In this thesis, the author robustly connects the color-magnitude diagram to SN Ia spectra and their physics for the first time, and shows that for the SN sample in the dissertation, this feature is important to consider as a contributor to scatter in the Hubble residual. There is no prior work in the literature that examines this feature in such depth, and it is rare to be able to paint such a thorough picture in a SN Ia study rooted in a single photometric feature. This work opens up many avenues for future observational and theoretical studies.