You hit the nail on the head Peckish, when I would wander off the blue line with the stitches the marks came out but when I sewed over the line then it stuck. I have washed the quilt 2 times letting it air dry each time. I haven't let it soak overnight, so I think I'll try that with the OxiClean. But first I will call the company and see what they have to say. I must say it is a real bummer but a good lesson to learn. Never use a new product on a whole finished quilt without having tested it on some scrap fabric. One lesson I don't think I'll forget anytime soon. :(

I don't have an experience with this marking product specifically but with other stubborn standard #2 pencil lines, I've taken liquid dish soap, thoroughly wet the area and then 'scrubbed' with an old toothbrush. Rinse and repeat as necessary.

Wishing you luck.

I hope you'll post any info from the company. Last night I went looking and found one of these markers in my marker drawer. I threw it away.

Two items mentioned (Oxi-clean and Dawn dish soap) have to be the best items to remove markings on quilts or stains on fabric. What would we do without them??

Try SewClean, it can be found at some Quilt Shops, I asked my local quilt shop if they could get and they ordered it for me, great stuff. You can tell your Quilt Shop that Checkers carry it. Checkers is a quilt store ordering house.

My go to spot remover is Grandma's Secret Spot Remover, which can be found in fabric shops, ei: Hobby Lobby. I use it on my quilts and laundry to remove all kinds of stains.. I will remove sharpie ink.

I second P-BurgKay's comment. I have had very good luck with Sew Clean for various stains, including pencil marks.

Hmmm, hard to tell for sure by the picture but it looks to me like you may have had transfer of the marking tool to your thread and the coloring is embedded in the fibers of your thread. To tell for sure is to take out some of the quilting and see if the mark is still on the fabric or there is actually color residue from the pencil in your thread. I had that happen to me once and nothing got it out until I ripped out all the quilting. Then the marks were gone because they were in the thread, not the fabric and I requilted.

I had dark mechanical pencil stains on a quilt (I thought that I couldn't see them if I did them lightly--Duh!). I was told to dab them with Lestoil (found at dollar store) and rub with a old toothbrush..It worked pretty well. If you Really look and know that they are there, you can still see some lines. Might be worth a try.
Otherwise, I would say that it was worth the few dollars that I spent.

You could try a Mr Clean Magic Eraser..dry.. if that doesn’t work, try wet