The Chromosphere is the layer of the Sun's Atmosphere outside the Photosphere and inside the solar transition region. It is about 2000 kilometer's deep and its density is a hundred millionth that of the Earth's atmosphere. The inner boundary is 6000K and the outer boundary is 35000K.
The chromosphere is visible during a solar eclipse.
The term Plage is used for certain kinds of bright regions of the chromosphere. They occur near Sunspots.