Top panel: light-curve decline-rate parameter, Δm₁₅, plotted as a function of wavelength where the effective wavelengths of the CSP passbands are indicated by vertical lines. At optical wavelengths the blue bands exhibit larger Δm₁₅ values than the red bands, while in the NIR Δm₁₅ is similar among the different bands. Bottom panel: same as in the top panel but with all SNe plotted in one panel, along with a low-order polynomial fit (solid red line) and its associated 1σ uncertainty (≈0.2 mag; dashed red line). The functional form of the polynomial fit is given by: Δm₁₅(λ) = −11.88λ⁵ + 63.74λ⁴−134.17λ³ + 138.81λ²−71.00λ + 15.00. Here λ is in units of μm and Δm₁₅ in units of magnitude. Shown in blue is a polynomial fit obtained from the same analysis of the SDSS-II SE SN sample (Taddia et al. 2015).