Thousands of books were coloured after printing - by publishers, artists, or readers themselves - but when and why was this done? Using non-invasive pigment analyses (FORS and MAXRF), the project links the timing of interventions to discourses on skin tone, flora, and visual conventions. Focusing on Dutch collections, it shows that colour not only enhanced illustrations but actively shaped early modern visual knowledge production, offering new insight into how colour informs historical imagination.