Connections between SN Ia light-curve stretch (x₁), global stellar mass (log(M_*/M_⊙)_global), and local environmental colour ((g − z)_local), illustrating the complex correlation between stretch and SN environmental properties. Left: Local colour vs global host stellar mass. The light grey band shows the 25%–75% percentile range for host global mass (vertical, [9.5, 10.5] dex) and local environmental colour (horizontal, [0.7, 1.3] mag). These cuts are used to select SNe Ia shown in the right panels. Top-right: Local environmental colour and SN stretch distributions for SNe Ia whose host global mass is in [9.5, 10.5] dex. Blue and red histograms show locally blue and red environment SNe Ia. The black histogram is the local colour distribution for the full sample. Bottom-right: Global host stellar mass and SN stretch distributions for SNe Ia whose local environmental colour is in [0.7, 1.3] mag. Purple and green histograms show low and high mass hosts SNe Ia.