Reading suggestions...and all good but did NOT work for me...I used blue chalk pounce and it did NOT come out. The company making the pounce/chalk suggested using vinegar which set the blue dye even more on my white quilt...ugh! She had me send the chalk and pounce back and never even replaced the $13 pounce. Tacky, at best.
I tried EVERYTHING...Synthropol, Retayne, Grandmas Stain remover, etc, etc.. Got a nod from a quilt restorer on what would work
WHAT WORKED: Washed in oxyiclean and did not rinse well, put some oxyiclean light paste that I made up over the worst of the areas, then put is out in the sun on thick grass...some air underneath... several hours....then washed again and did not machine dry. I did this a couple of times and it was almost completely out. Then I started using it (instead of a wall hanging) as a table cloth on my breakfast table and found that after several more washings (no heat dry), the blue chalk from the pounce was completely gone... I can now machine dry.