Ok here is the second installment in the things I did not understand from the blender manual and the gamekit book.
In the explanation of the face buttons the manual and the game kit says about the Add button.
Faces are rendered transparent. The color of the face is added to what has already been drawn. Black areas in the texture are transparent, white are fully brite. Use this option to achieve light beam effects,glows or halos around lights. For real transparency ust the next option “Alpha” "
Ok I understand most of this. But WHAT color. The material color of the mesh? The vertex paint color you are applying with the brush? What.?