How to assign different materials to different colors in a texture? I just started using blender a few weeks ago, and am almost completely new to the node aspect of it, so I am not even sure if this is possible.
One of my objects is meant to have blood on it, and while I am not going for photo realism and this will be fairly far in the background, scribbling red on it in texture paint makes it look horrible. My main problem is that the blood is metallic and sparkly just like the steel material:

Is there any way that I can have a differing material depending on what color the texture is?
You can make a mask texture. This kind of map is black and white, where black means 0, and white means 1. So if you plug it into a Mix Shader node with your blood and steel materials like so:

The black areas of the mask texture will indicate steel material, and white will indicate the blood material. So paint the steel portion of your mesh black and paint the blood portion white, and they will have separate materials.