SOMETIMES MY MELT AND POUR BARS GET A BROWN RUSTY LOOKING SPOTS ON THEM--IS THAT FROM THE VANILLA FO-OR AM I DOING SOMEHING WRONG?
I am not sure, but I have a couple of thoughts;
1) If the Fo has a color, are you mixing it well?
2)Are you using a metal mold? If so, it could be rusting. (I recommend silicone muffin molds- they do not rust and it is easy to remove the soap.)