I just finished a quilt that had a black sheet for a backing and I used Hobbs 80/20 in black. I was afraid that some white might poke through. It was a special quilt for a customer so I wanted to be extra careful.
I also did one that had a solid black backing and used white poly (Quilters Dream) on it and it was perfect, no white on back!
Last week my daughter quilted one for her friend and the backing that her friend had was very thin muslin-like black and she had sent some thin white cotton batting. She did get some white pokes on the back.
I think that the backing has something to do with the white coming thru because it was so thin.