Our house has a white flocked ceiling, which is pretty nice. In the
areas right around the ceiling HVAC vents, the flocking has gotten
discolored over the years, partly because of dust that can be vacuumed
off, but partly because of dust or stain that will not come off that
easily. What are my options?

I'm pretty sure I can't just wash this stuff. Much too delicate. I
really don't want to scrape it off and reapply. Partly the bother, and
partly because any freshly flocked spot will almost certainly look
mismatched. No, I DO NOT want to redo the whole ceiling!

Light touch-up with flat spray paint? Spray on some bleach? Similar
concerns about mismatching, but there are strategies for trying to
make it blend in with the rest of the ceiling. I'm not looking for
perfection, here. Just a cleaner ceiling.