Hopefully you didn't put them in the dryer. The dryer set the color and it is harder to get out. First I would soak them in white vinegar overnight. If that doesn't work use a fabric bleach that is safe and do the same thing. This might take a few tries.
Well to fix this just soak and wash them in some bleach. Eventually it should get them back to white again. The darker they are the longer it will take. Also make sure the fabric is safe to bleach.
