I've made my dingy white thread into black that way, but if you're tying jigs for profit, it's absolutely not worth it (at least to me). Maybe if you just tie a few jigs a year for personal use, and you only want to have one color thread, but then you have to have sharpies too, and we all know how fast they disappear. I'll just throw a spool or two of thread onto all my orders to make sure I have my colors on hand.