Around the turn of the seventeenth century, a variety of authors writing in Spain invoked the shifting chromatics of iridescent materials—whose colors appear to change with alterations in the geometry of illumination or view—to teach audiences about the world in which they lived. While some of these texts drew connections between fluctuating hues and the mutability of the earthly realm, others saw parallels between the same vibrant visual effects and the nature of the divine. This article examines how authors exploited the pedagogical potential of iridescent materials to teach lessons about Catholic doctrine, both by navigating the semantic variability of iridescence itself and by breathing new life into the venerable philosophical traditions that made meaning from it.