Many of the "signs and tokens" described in alchemical texts relate to colour, from the Crow's Bill signifying putrefaction to the philosophical solvents disguised as Green Lions, Red Dragons, and Grey Wolves. While the process of yellowing, or citrination, often appears in medieval recipes, it seems to have interested commentators less than the more familiar processes of blackening, whitening, or reddening. Yet beyond these canonical colours, yellowness turns out to be ubiquitous in alchemy and its associated craft practices, both in Latin texts and vernacular translations. This paper uses source criticism and experimental reconstruction to interrogate the role of yellowness at the beginning, middle, and end of practice, focusing on fifteenth- and sixteenth-century England. As starting ingredients, yellow vitriol and litharge offered the potential for transmutation but also posed problems for identification and preparation. As an intermediate stage, yellowness offered promising signs of future success, in the form of dramatic colour changes and unexpected products. But yellowness also offered an end in itself, as appears from the many citrination processes attested in recipe collections which aimed to imitate the properties of gold - suggesting that yellowing was prized as a significant indicator of chemical change across diverse areas of craft practice.