I used create from bone heat and the models arms deformed poorly, so I went to weight paint to see and repaint and the mesh was black not blue . I can see a slight shade of blue and red where there is weight but it is almost black. i changed view port shading, shader, add lamp. painting mask helped a little but I can not get the normal blue . I cant see it well.
I know this thread is a couple of days old, but this seems to be a rare problem that I’ve figured out before… Check the scale of the mesh. The mesh should always have a scale of 1 in the x, y, & z. If the scale is set to -1, this black mesh when weight painting occurs… Another thought, and I don’t know how much it might affect it is the normals, make sure they are all pointing outwards…