Hubble PaletteMapping Hα, O-III and S-II to red, green and blue is problematic when two of them are red, one is green and none is blue. Astronomers deal with this by using false colour — one or more of these elements is going to have to take a hit for the team and take on an unnatural hue. The Hubble palette assigns red to S-II, green to Hα, and blue to O-III: red is accurate, green and blue are false.
The elements there are sulfur, hydrogen, and oxygen.
There is a representation issue in “boring” or cool astrophotography. A lot of interesting phenomena are not visually interesting. In the Hubble’s case, colors are remapped for informational purposes, but it can’t also help but “sell” space to people.