Roxanne, what colour is your background fabric. I will tell you what I use on my black fabric. The white pencil that you use to make your nails white underneath. It works a treat on black and it rubs off with an eraser. I just keep it nice and sharp and get a great white line.
Another trick I have when I am marking my embroidery lines I place the pattern on top of the fabric and using a thick needle the kind you use for darning, or upholstery stab through the paper and the fabric it leaves holes all the way around where you mark the embroidery. I then use my pencil to join up the holes which eventually disappear.Use the same trick when I have a fabric on top of a fabric to place one on top of the other. Makes sense????