How Texture Paint over assigned material I have a problem with painting. I don't know what am i missing.
The mesh becomes black and the colors do nothing when i try to paint on it. 


Also is it possible to assign a diffuse color and to paint over the material like this?
You have your image texture also loaded as a brush texture, so you are painting black on black. Press the little X to remove the texture from your brush and see if that doesn't help.