Dawn is not recommended for removing pencil marks. I hate to say this but those yellow lines - tho faint) may be there forever. I don't believe it is ever a good idea to use the colored chalk in whatever way it comes - chalk, pencil. I tried bleaching some yellow out of muslin one time - a pencil that supposed to be washable and it never came out of the muslin. Test first is always a good idea - never trust the manufacturer. Test it for yourself. These marker can react differently depending on the fabric.