HI use them quite a lot, HOWEVER, I did have one bag where the red pen did not go away when I ironed it...is in the lining and doesn't show, but I can see it! And on some dark purple handles I used the red one (again) on I have a white line left after ironing. I am going to try washing....again it's on the underside and really isn't major, but there!
I have had no trouble at all with the blue, black, or yellow. Just red and me have a thing!