Oh, don't you make life harder? =3=

Give or take a few numbers around. No need to follow these exactly. (For example, instead of 100, you can try 90.)
Hot and Sunny: +100 to colors, don't change grey
Heavy Rain: -25 or less,-25 or less, -25 or up, 0
Light Rain: -10,-10,-10 or up, 0
Night: -50,-50,50,0
Day Time: No tint
Morning: +20 to all colors?
Snowing: Do what you feel. It doesn't get dark while snowing though.
I don't know if these yield awesome things. You have to just keep trying. Don't be afraid to go to extremes.