Atmosphere -> Main -> Bluesky horizon colour
Atmosphere -> Tweaks -> Bluesky density colour
Set the second to red, sky becomes red. Set the first to green the sky becomes green ignoring the red in the second.
Is there a difference or is it another light bulb with 2 switches?
If you set the haze density to 0, you'll see that the combination of red and green that you entered produces a black sky.
The turquoise that you see when you add haze to this is because the haze is grey and it's being lit by sunlight decayed by a turqoise decay colour (which is the complement of the colour you chose for bluesky density colour).
If the linking of bluesky density colour with redsky decay colour seems like a limitation, then don't use bluesky density colour, use bluesky horizon colour instead. But there are times when it's useful to have that control.
Experimenting with haze color itself brings also interesting results.