Unfortunately some colours are not colour fast. The darker and more neon the colour the worse they can be.
Your best bet is to try and make the hair colour fast - you want to soak the hair in a cup of cold water in which you have dissolved a tablespoon of salt and 3 or 4 tablespoons of vinegar. Just leave it soaking and then rinse out, allow to air dry. In order to test if its fast, just wash with warm water and drag the hair over a piece of white kitchen roll.