Mesh Painter won’t actually change the textures on the mesh. How it works is by applying an overlay mesh to the object for painting to.

The program has been found to fail on certain meshes, whereas it works fine with others. Please start a new project and add a standard cube to the scene to test the painting before trying on anything more complicated.

Due to instances where Mesh Painter has been known to crash Unity please also save your scene and backup your work before trying this program.

These issues will be addressed in a future release, but since the program was never intended to be a serious painting application, rather than just a fun graffiti tool, there are other programs that have a higher priority.