A lot of these pictures are presented in black-and-white. In some case the "base" picture was monochrome, but often they've been rendered in grayscale because of the problem of the color of blood.

Convincing blood and real blood, oddly, do not necessarily look the same; blood changes color with lighting in a way few other substances do, appearing virtually black in moonlight, for example. Beyond that, blood drawn from different sites has different colors; arterial blood may be brilliant red, venous blood purple, abdominal blood pinkish (due to mixing with other fluids) and pulmonary blood foamy and pale (from aeration). It may change color quickly, too, on exposure to air or while drying--and some drying occurs within minutes. In certain lights, too (sunlight especially), fresh blood has a distinct "wet" look, but this may disappear completely if the lighting changes, making it look flat. Stage blood, made using red and blue dyes, looks more "real" in most photos.