Blood hasn't always been red.
Not in the movies, at least. Before the advent of colour, blood oozed black like sin from the enemies of James Cagney. Black as ink, black as the lost souls of 1930s Hollywood cinema.
In 1957, Hammer Studios released The Curse of Frankenstein in Eastman Colour. Reds blazed from the screen with lurid intensity.
For a good thick dollop of Kensington Gore, mix one part water with three parts corn syrup. Drip in some red food colouring, and maybe some blue. Stir in corn starch for a nice claggy texture.
Or, if you haven't time for that, do what Alfred Hitchcock did when shooting Psycho. Film in black and white and use chocolate sauce.