I have used blue chalk but I lighten it with white and vaccum it off.

I use regular children's colored chalk. It fits in pencil sharpener to make a sharp point. No problem with it brushing off the fabric of any color that I've tried so far.

My avatar quilt was ruined with the yellow dritz chalk. I've tried everything suggested so far and the yellow is still there, but is fading over time with use and washings. Hopefully someday it will completely fade. I've switched to water soluble markers that fade with water. Good luck.

Thank you to everyone who has replied to this thread. I think I will be staying away from all colored chalk. Everyone else's experiences is enough to scare me away from them.

I too used Dritz chalk to mark on granddaughters quilt. After washing the finished quilt on Delicate cycle, cold water, I couldn't believe my eyes! Chalk was still there. What worked was washing quilt in sink using Fels Naptha bar and gentle scrubbing. It came off, but not sure I'll ever use chalk again.