Along these lines..

Non‐melanotic discoloration of the skin can result from the accumulation of various internal agents (ingestion, inhalation, or injection), chemicals or drugs, such as heavy metals, amiodarone, tetracycline, clofazimine and others, or exogenous (topical) substances. Identifying the causative agent frequently requires a thorough investigation and clever detective work, including visits to the home and workplace. It is, however, rare that the patient presents at a clinic with the corpus delicti, and it is even more rare when neither the patient nor the treating physician are initially aware of it. “What is the hardest of all? That which you hold the most simple; seeing with your own eyes what is spread out before you.”[J.W. Goethe quoted by J.P. Eckermann in Converstions with Goethe, May 18, 1824.]