This section is from the "A Handbook of Useful Drugs" book, by State Medical Examining and Licensing Boards.
The following classification is taken from "Introduction to Materia Medica and Pharmacology" by Oliver T. Osborne.
Drugs and Preparations Which May Cause an Eruption on, or Itching of, the Skin: Antitoxin Arsenic Belladonna Bromids Chloral Copaiba Iodids Opium Quinin
Salicylic Acid Synthetic Compounds Volatile Oils, and drugs containing them.
Drugs that increase its amount cause it to be lighter. Drugs that irritate the kidneys cause it to be darker. Methylene-blue causes it to be green, if acid. Phenol may cause it to be brown (same appearance as bile). Santonin causes it to be yellow, if acid; purple, if alkaline. Senna may cause it to be red, if acid; yellow, if alkaline. Sulphonal may cause it to be very dark.
Bismuth salts color them black or dark gray. Colchicum colors them greenish. Iron colors them black. Mercury colors them green. Purgatives cause them to be darker.