If your shirt is cotton or other fabric that can be bleached, I think you would have to remove the color from the fabric first, then tie dye it. Buy some color removal and follow the directions on the package. It may not come out completely white, but it should be light enough to tie dye. I am not an experienced tie dyer, but I imagine there are lots of directions on the internet and in various books on the subject. Good Luck!
DYI LiLa, January 2011
