I have been using Crayola Washable markers too. I usually mark my quilting lines with them and have been doing mostly QAYG blocks so sometimes they sit for a while before assembling and finishing the entire quilt. I don't mark them lightly either -- I use a ruler and really draw on them so I can see where I'm going when quilting. By the time the finished quilt is washed, the marks have been on the fabric for quite a while and have also been ironed several times as well! I don't know if it matters, but I use all 100% cotton fabric, thread and batting (no poly or blends). I've used almost all of the colors and have found no difference -- they have all washed out without a trace. I love them and they are probably one of my least expensive quilting "tools"!