Difference between contusion and post-mortem lividity is that post-mortem lividity: (A) Shows sequential color change, (B) Easily washable, (C) Shows diffuse irregular margins, (D) Has raised enzyme levels
Answer is B. The synopsis of forensic medicine & toxicology; Dr k.s Narayan reddy; 28th edition;pg.no. 88; 
Contusion or bruises are not washable but postmortem lividity is washable.