Sève de porreau (French: "leek sap") was one of many plant-juice greens used in medieval manuscript illumination when more permanent mineral greens were unavailable or too expensive. The medieval illuminator's palette included numerous fugitive plant-based colours — many manuscripts have lost all green passages to fading, leaving only the underdrawing.

Ephemeral, botanical, and intimate. This colour exists as a historical footnote — a reminder that medieval artists worked with whatever materials were available, sometimes accepting impermanence as the cost of having any colour at all. Its very fragility reflects a different relationship with time than modern permanent pigments embody.

The use of leek and iris juice in medieval manuscripts reflects both the ingenuity and the limitations of pre-industrial pigment making. Medieval artists were simultaneously scientists, chemists, and craftspeople — grinding minerals, extracting plant dyes, and mixing animal-derived binders. The reconstruction of medieval pigment recipes has become an important field of art historical research.