Deep blue colour of hypostasis is seen in death due to poisoning by:
Potassium cyanide
Phosphorus
Aniline dyes
Carbon monoxide
Aniline dye poisoning causes methaemoglobinaemia which gives deep blue colour hypostasis after death. Other poisonings which cause methaemoglobinaemia are, nitrites, potassium chlorate, potassium bicarbonate, nitrobenzene, acetanilide and bromates. Ref: The Essentials of Forensic Medicine and Toxicology By K S Narayan Reddy, 27th Edition, 136, 137,139