Could you add a picture of what you would like to achieve? If your hair is too porous to bleach I wouldn't suggest using any more oxidative dye. Depending on how dark you want it you could either put a diluted semi-permanent purple dye on top of what you have or if you wanted a slightly more vivid color you could use a color remover (not color stripper) and then apply your dye. Obviously the darker your base hair color the darker your result will be.
