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.