Dust Alone Explains Nearby Supernova Color Scatter, Easing One Cosmological Tension

A new preprint posted to arXiv on 4 June 2026 uses two large, homogeneous low-redshift samples—the Zwicky Transient Facility DR2 and the Foundation DR1—to argue that all observed color-magnitude scatter in Type Ia supernovae arises from dust rather than intrinsic SN properties. The authors apply the Bayesian hierarchical model Simple-BayeSN to roughly 1,200 spectroscopically confirmed events and show that previously reported intrinsic color correlations vanish once selection biases from traditional color cuts are modeled. This directly challenges the long-standing interpretation that part of the Tripp linear correction reflects progenitor or explosion differences. The work is a preprint and has not yet undergone peer review; its conclusions rest on low-redshift data only and therefore cannot yet address possible redshift evolution of dust properties. Earlier analyses, such as those in Mandel et al. (2017) and the DES-SN3YR cosmological sample, left room for a 20–30 % intrinsic component; the new modeling attributes that residual entirely to unrecognized selection effects. If confirmed, the result strengthens the empirical validity of the Tripp relation while relocating its physical origin to host-galaxy dust, thereby reducing one systematic floor in dark-energy equation-of-state constraints. It also implies that the well-known host-mass step may itself be a dust-metallicity correlation rather than an intrinsic luminosity difference, a possibility only briefly explored in the current analysis.