To use dark dye on bleached hair, it should have been at least 2 weeks since you have bleached your hair. Also, the hair should be in good condition. The best dark dyes to use would be temporary colors in order to avoid extreme drying. Hennas also work to darken bleached hair.
You can't use black because your hair will turn green. You would have to use a medium brown on your hair. Do a strand test on a patch of hair that will not be seen so that you can get the desired result. Going to dark will ruin your hair.
You can use dark dye on bleached hair, but it depends what your trying to conceal. Did you bleach your hair only to find that it's now a nasty orange? If you apply a dye any lighter than dark brown it will appear red or copper. Buy a box of color oops.
If you bleached your hair, and now you want to go back to a darker color, yes you can do that. It is a two step process, and you will need auburn hair dye, and a light brown dye to do it.
