Getting color right can be very tricky. I tend to stick with atmosphere defaults until near the end of a project and then adjust them if I feel they're not yet getting me the tones I want. This is largely because the defaults give pretty realistic results in most real-world situations of scale, etc. I don't know if you've done any such adjustment already, but if so it would be worth trying with just a default atmosphere and sun/lighting setup just to see what it looks like for "reference" of sorts.
Also, of course, if you have the ability to verify calibration of your monitor that's always important to do.
- Oshyan
