Extreme-ultraviolet Imaging Telescope (EIT), observing the Sun in Fe XII at 195 Angstroms. Light at this wavelength is chiefly emitted by Fe XII (iron ionized 11 times) at 1.4 million degrees K.
Because very little UV light penetrates the Earth’s atmosphere, we have to go into space to take images like these. It is not possible for the human eye to see ultraviolet light directly. Thus, the colors of these images are just ways to represent them so we can see them. To keep the images straight, we assign certain colors to EUVI images taken in particular extreme ultraviolet (EUV) wavelengths, so usually the 195 Å images are in green.