Had ferns inside all winter. Put outside when good weather but overnight there was a light frost. Fronds are dark green some just half way. At the base of the pot they are still nicely green. The roots did not get it and there are about 1/3 of the fronds that escaped any harm. Will the dark fronds come back? Did not cut any back.
Since only the foliage was frosted, I would probably wait a bit to see what does not recover. For those fronds that have been damaged, and don't recover within a few days, I would trim back the damaged area, leaving the good to continue to photosynthesize. The fern should respond by sending new growth, probably pretty quickly. As the new growth emerges, you can begin to remove the remainder of the damaged foliage. Since it was only a frost, not a deep freeze, the plant should be fine. Perhaps give it a bit of fertilizer when you water it next.