Quick and easy (probably). Got a mesh, want to polypaint a pattern onto it that I've made in Photoshop, saved as a jpg. Load the texture (black and white), add to spotlight, turn on polypaint and set my brush to RGB only. When I paint there is no black paint applied below. There's just nothing. Am I being stupid here and…
Black acts as a mask, so those areas wont get painted. You're left trying to project white polypaint from the spotlight image onto the model, which you probably wont see unless the model is filled with some color other than the default white.