I have one pony I used black RIT dye on that did bleed in to the hair, but I had a sneaking suspision that it was going to do that so I only put in one plug and waited, lol. If you are worried, just do one plug of hair and then set it aside for a week and watch what happens. That way you don't mess up a lot of hair. If it does start to bleed, I would try washing the pony in really cold water to help set the dye. After that, do another test plug.