As you can see in the pictures below, mouth is red, face is beige, and I want the selected lip faces to blend the two colors gradually.
How? I’ve tried doing a UV unwraping and color ramping.
Your best bet would be to create an image mask with a graded edge - then use that to mix between the two materials.
What about image textures on each face?
Would be a bit tricky. If you have already UV unwrapped - then just use the UV map and create a texture - or use the texture paint function to create the mask.