I know a gal and I myself have done this; when using chalk test it on a dark fabric, wait about 30 minutes and go back to wipe it off with a piece of felt like they use on old chalk boards. It usually comes right off if it hasn't gotten wet. 100% wool yarn will do this also. Shouldn't have a problem. To make colored chalk usually a dye is mixed in that at some point was wet. So when chalk gets damp it has a tendency to set. My cousins kids used to draw on their driveways but they first used a broom to brush it off before hosing the driveway to clean. Have you ever noticed how much easier it is to sweep flour excess than it is to mop?