OK, it's entirely possible I have finally found my holy grail when it comes to marking dark fabric.
It's a Bohin Mechanical Chalk Pencil. I bought it Sunday at a quilt shop. I had seen it on the internet, but I hesitated about ordering it. I bought white, but I think you may be able to get other colors of refills.
It kind of rubs off, but not enough so that I can't see it at all. I don't know if I could mark a whole quilt top at once, but with a stencil, it would be easy to mark as I went along.
The thing is that it is soft chalk and it doesn't distort the fabric. It has an eraser that completely erased the mark.
I've tried other chalk pencils and they just don't do it for me. I didn't really care for the Clover white pen either.
This could work. I'll keep you posted.
Cindy