In the 14th-century apple pie recipe, saffron colors the filling.
The recipe appears in The Forme of Cury, an English cookbook associated with the cooks of Richard II. Its apple preparation combines apples with other fruits and spices inside a pastry casing called a cofyn. Saffron is specifically identified as the ingredient that gives the filling its color.
Saffron was prized in medieval European cooking not only for its warm yellow hue but also for its distinctive aroma and prestige. It was an expensive spice, so its presence signals a dish made for an affluent household or an important kitchen rather than an everyday inexpensive pie.
Modern cooks may mistake turmeric or paprika for the answer because they are familiar coloring spices today. Annatto can also tint foods, but none of those is the ingredient named in this medieval recipe. The recipe is an early ancestor of apple pie, though its fruit-and-spice mixture differs from the sweet, apple-dominant pies common now.