No. Sun-in will only work on virgin hair (undyed). Sun-in is simply a weak peroxide solution and since you used a stronger peroxide (developer) to put the color into the hair, it makes no sense to think that it would take it out (and it won't).

I'm afraid I can't agree with the opinions expressed above. You won't have to bleach it (unless you want to). You have many, many options to lighten it that are much less damaging than bleach. You said you used Nice 'n Easy, so it's not a semi-permanent (though ingrid119 is correct that shampooing frequently will cause it to fade -- even though it's a permanent). Beauty Expert is correct that haircoloring alone won't lighten it -- but you know about ColorFix.

Why did you dye your hair black if you want it light ash brown? I suspect that you wanted something "different".

If your hair is so porous that it's "grabbing" color, then it will fade -- and probably within a few days. You can also "spot tint" the uneven areas.

You can try ColorFix again. Then, when you dye your hair again, recognize that your hair seems to be particularly porous and use a much lighter color -- and stay away from black. Do a strand test to make sure of the color you'll get.

Also, realize that all this will damage your hair -- at least make it dry. You may not be able to do many more chemical processes without risking breakage.