I think the diff. shades just came from how much bleach soaked into each spot. You know, you bunch the shirt up in several places and put really tight rubber bands around each part. The darkest purple was the original color of the shirt, and none of the bleach water got in there because the rubber bands kept it out. It's just random and has to do with luck, I think! I just filled the sink with some bleach water and submerged the whole shirt. I had to leave it in there for awhile before anything happened. I didn't think it was going to work at first. I tried this on a red shirt and absolutely nothing happened. So I think it depends on the kind of dye used on the shirt when it was first made. Just experiment, it's fun, even if it turns out bad!