How about a religion that worships color? The people believe that there is a specific spirit within each type of color. If there is a blue cup and a blue flower, both would be inhabited by the same spirit, but if there was a blue shirt that was even slightly different in shade of blue, there would be a different spirit. The strength of the spirits is based upon how pure the color is.
The pure colors (red, blue, and yellow) are the most powerful of spirits while green, purple, and orange are next in power. As colors become more of a mix, the spirits inside of them get less and less powerful.
There are numerous factions within this religion that are at constant war with each other. The three main factions are obviously for the spirits of red, blue and yellow. The worshipers believe that the spirits have called on them to get rid of all opposing color.
So, the worshipers of the red spirit will wear all red and their temple is completely red... you get the idea. Part of ridding the world of opposing colors involves assassinating priests of opposing factions. If the red priests catch anyone, they will open all the veins, making a lot of blood come out, and then they will spread that blood all over the captured persons (naked) body.
The blue priests wear all blue, etc. They kill their captives by drowning them in ice cold water...
Right now I'm not quite sure how the yellow priests kill. One idea is that they put captives in a cage out in the desert, letting the (yellow) sun kill them. That doesn't follow the pattern of turning the body yellow, though. They could paint the bodies yellow, but that would be too easy.
This was a really weird religion idea, but it seemed to me that if people can find spirits in rocks and such, why not take it one step further and find spirits in the colors, themselves?
And I apologize for my poor writing style.