You might want to try shooting in RAW mode, and then you can adjust the white balance, either in the camera software or in Photoshop. You can see what effect that various white balances have on the overall composition. I am assuming that the D100 is similar to the D70, so you may want to try shooting in a Programmed Mode, with everything on auto and RAW format. That way you can see what settings the camera thinks it needs and compare to what you have been using. That may give you some ideas on what settings you might tweak to achieve better outcomes.
You did not specify whether you are metering to a gray card, when shooting in shady conditions. If you don't have an incident light meter, that is an inexpensive way to see if you are metering properly.