  Phase imaging is gaining importance due to its applications in fields like
biomedical imaging and material characterization. In biomedical applications,
it can provide quantitative information missing in label-free microscopy
modalities. One of the most prominent methods in phase quantification is the
Transport-of-Intensity Equation (TIE). TIE often requires multiple acquisitions
at different defocus distances, which is not always feasible in a clinical
setting. To address this issue, we propose to use chromatic aberrations to
induce the required through-focus images with a single exposure, effectively
generating a through-focus stack. Since the defocus distance induced by the
aberrations is small, conventional TIE solvers are insufficient to address the
resulting artifacts. We propose Zero-Mean Diffusion, a modified version of
diffusion models designed for quantitative image prediction, and train it with
synthetic data to ensure robust phase retrieval. Our contributions offer an
alternative TIE approach that leverages chromatic aberrations, achieving
accurate single-exposure phase measurement with white light and thus improving
the efficiency of phase imaging. Moreover, we present a new class of diffusion
models that are well-suited for quantitative data and have a sound theoretical
basis. To validate our approach, we employ a widespread brightfield microscope
equipped with a commercially available color camera. We apply our model to
clinical microscopy of patients' urine, obtaining accurate phase measurements.
