lsscpp is right that the colour ramp is not ideal for this, in my first attempt I was simply tinting the sky.
After a few experiments I have come up with this:
As it is it does nothing but you can now change the input colour per rgb channel and get some realy interesting sky colours. It will also change coulors with the air settings etc and respects the light values.
Here I have changed the colours a bit.
Here is the file if you do not want to copy the nodes!
NishitaColourChange.blend (853.1 KB)
You can now change the colours to your hearts desire 
This was fun, happy blending!
Edit:
I have now added a saturation control per channel, I will defiantly make use of this setup. I have updated the file.
