The Colour of Blood is a portrayal of the Fear of Temptation from The Rapture Cycle. She is the head of the Red Fears, the sister of the Devil, hostess of Tuonela, and appears in the form of a universe who can shapeshift into anything she wants, though as the stories are from the perspective of humans, she usually manifests as a human.
The Colour of Blood arrives with the rest of the Red Fears at the end of September, as The Lamb blackmails her to assist in Rapture's terminal coming. She tempts Jordan away from Salmacis and towards suicide.
In October, she turns on The Lamb and helps fight it off for good.
In The Cockroach Metamorphosis
As a fixed member of the post-apocalyptic pantheon, The Colour of Blood actively defends Earth from foreign invaders, and she seeks to protect her brother at all costs. Her universe allows Tiresias to travel through time. Salmacis beats her in a duel in Part 3, killing her possibly for good.