What kind of gas would have to be in Earths atmosphere to change sky color to green?
The blue of the sky is NOT due to any color of gases in the air. Both nitrogen (80%) and oxygen (20%) are colorless. The blue of the sky is due to something called Rayleigh scattering. There is no way that the scattering could appear green to our eyes unless only green color was hitting the sky from the sun. If the sun were emitting only green color, the planet would not support life as we now know it. What the question probably meant was “Name a gas which transmits green light. Could you breathe it and live?” You can get an answer by looking up the colors of the halogens.
