Soft torsos, both Obitsu and Type 2 pullips, are extremely prone to staining. All bodies will stain, if put long enough in clothes that haven't been colorfasted, but even a couple of hours in one outfit will do it for soft torsos. This method will remove the stains from pretty much any doll body.
Warning: you need to be very careful with this technique. Not only does zit creme remove stains, it also can suck the color right out of the plastic. For this reason, I recommend using it sparingly, precisely, and checking often.
This torso is a good example because it has two kinds of stains. It has black solid stains, and general area dye stains (the yellow). Any brand of zit creme will do it, if you have one on hand you can use that. I just bought the cheapest brand at my local store.
Solid stains are usually caused by reds, blacks, and dark blues. They take longer to get out, and are fairly common on type 2 pullips straight out of the box; Fourrure and China China usually come stained. To treat these, put a bit of creme over the stain, getting as little onto un-stained areas as possible. After you lay the doll out in direct sunlight, check it about once a day by removing the creme and then reapplying to the areas that haven't been de-stained.
General area stains are usually caused by lighter colors and are less hard to get out, but can be trickier. They're usually larger, and so there's a bigger chance of bleaching a big white spot into your doll. Use a thinner layer, and check more often. Once the stain is almost gone, take the creme off but leave the doll in the window for another couple of days. The creme will keep on bleaching the body after it has been removed, even if you take it out of sunlight. If after a few days the stain is still lingering, you can treat it again.