The chromosphere is a thin layer of a star's atmosphere, just above the photosphere and below the corona.
In 2153, Captains Drennik and Jonathan Archer explored the chromosphere of a hypergiant in a Vissian stratopod. (ENT: "Cogenitor")
In 2368, the USS Enterprise-D hid from a Borg scoutship within the chromosphere of a nearby star. (TNG: "I, Borg")
In an alternate timeline where humanity was almost destroyed by the Xindi, Yerdrin Lek hid his ship just above the chromosphere of Ceti Alpha while spying on Phlox and the colony on Ceti Alpha V. (ENT: "Twilight")