Update to my post above: After the first wash I could still see the black marks from the Sewline pencil, yikes!, so I sprayed them all with Spray and Wash and washed again. Unfortunately, I could still see them after the second wash. Thinking I was stuck with them, I put the quilt into the dryer, BUT, it came out of the dryer with no marks whatsoever! Yay!!!
I bought a pack of washable Crayola markers yesterday and tried all 8 colors on some all cotton Moda fabric. The colors came out with plain water. I may try them on a "practice" quilt to see what happens.
Hope someone finds my info helpful.
Jodie