I'd be surprised if the black leaves go back to green, I would have thought them more likely to wither and die. If you haven't used neem oil on a particular plant before, it is best to test spray a leaf or two and see what happens within the next couple of days or so. Neem oil can burn leaves on some plants. Whether it would look like that I'm not sure, it looked more "crispy" when I saw the burn on other plants once. One way to find out would be to spray one of the remaining good leaves while it is indoors, and see what happens.
