what a heartache! I have never used the yellow but I have had trouble with the blue pounce chalk in the past.. so I will only use white now

I was going to suggest Dawn dish soap - just like someone else did

I think the idea of hosing it down from the backside is an interesting idea - I have to remember that one :)

oh no, I feel your pain!! :(

I had the exact same problem with the blue pounce powder. It took me trying many different things to get it out.
What finally worked for me was a combination of "Mean Green" cleaning solution and Dawn dish detergent and an old toothbrush... and a lot of elbow grease.

Never again. And I will be adding the yellow chalk to my list of items to "never use on a quilt".

Good luck!!

Just an fyi: There's a white blacklight powder you can use on light fabrics. In normal lighting, the powder looks white, but when you darken the room and shine a blacklight on the quilt, the powder glows green, is very easy to see and follow. I use it longarming, and save $$ by mixing it with the ordinary white powder. Afterwards the powder brushes off or can be vacuumed, etc. just like any other powder. You don't have to have a longarm to use this powder when quilting. Try it, you'll like it!