|This is such a "duh" idea, that I'm not even sure it's worth posting, but here goes-- I use my son's Crayola washable markers for transferring pattern markings to my fabric. They come in many colors and always seem to be in abundance around my house! They are designed to be washable, and, although I have not ironed over any to check to see if this "sets" the ink, they do wash out of fabric easily with just water. I wouldn't advise using these on fabric that is not washable or is extemely valuable, just in case, but for everyday items that will be thrown in the washer, these colorful pens are just the ticket!
Edited to add: I just tested a navy blue pen today by marking a white piece of woven cotton & ironing over it with an iron set to "cotton" w/ steam & letting it cool. The mark washed out with cold water & dish soap, so it looks like these pens will not set when ironed. Score! ;0)