In restoring a bunch of old family heirloom photos, I came across a fair number of those that "barely showed and outline." They'd mostly gone to the "bottom of the barrel, but never got thrown away. Amazingly, about half of them came up to passable black and white, and a very few had enough color to make "fair" prints, when scanned at fairly high resolution and run through some of that "optimization" in Photoshop Elements.
If your film is too badly underexposed, you can't bring back color, but just because the print is "black" doesn't mean there isn't a picture there. Sometimes yes, sometimes no.
At Watering Hole 2003, there are about 4 "group pictures" near the bottom, of some of the pickin' gang, that I had to lay 3 or 4 layers of screen on to brighten up enough to tell that there was any picture, but the results aren't too bad. These were film shots, scanned (even though the prints looked solid black) and "brought up" digitally.