I'm having a proglem using the orange chalk on light green fabric. I think I have it out of the fabric (rubbed it with scraps of batting). Looks like it's still in the thread. I'm going to work on rubbing it out more and then use a Tide pen before I wash it. All that colored chalk is in the trash now.
I've used the purple air dry marker on white - it took well over a week to disappear! But it's gone completely and never came back.