Are you referring to hot peppers?
If so, is the black on part of the pepper but not sunken or mushy?
If so, this is a normal reaction. Sometimes things happen.

Oops. Just realized you said bell peppers.

Even so, it's likely normal. Difficult to tell without a description more precise than "spreading across my ... pepper plants."

Oh, dear, I may have unecessarily sacrificed on of the pepper plants.

We had three pepper plants in the garden, all sweet bells: one green, one yellow, and one red. They were very slow-growing, and I wasn't paying close attention to them. They started blooming the end of June, which drew my attention; then I noticed that there were black patches on some of the leaves, and even some of the flowers. I searched on "black spots" and came up with "black spot fungus," which looked like what I had.

The smallest and straggliest of the plants had black patches over so much of it that I just pulled it up and tossed it. I thought I could save the other two plants. I did get the fungus on the retreat, but then I got sick myself for a few days, and the next time I checked, the one developing green pepper seemed to have the same black stain growing across it.

There isn't any necrosis. Leaves that had the black spots on them, and weren't treated, would eventually wither and die. Blossoms that weren't treated would shrivel; the fruit bud, instead of developing, would dry up and fall off. The green pepper that had begun developing before it got infected has not died, nor has any part of it rotted -- though it doesn't seem to be getting bigger very fast, either.

For whatever reason, applying a paste of wormcastings and water has made the black patches on stems and on the fruit fade away. New growth is coming in that has no black on it.

My reasoning was that if this was "black spot fungus" the beneficial microorganisms in wormcastings would compete with it and drive it off. Maybe it isn't fungus, and the wormcastings have worked on it in some other way.