I've been playing with the SL Viewer's Environment Editor and I've customized my environment settings. Certainly, there are numerous combinations of light, weather and time of day to set up.
These changes are possible with all viewers. You only need to try and customize your environment to achieve more personal and evocative atmosphere when you are inworld.
I've just visited the Zigana Sim, a charming natural and rural place, where I've tried different settings setups.
Check out the following pictures but better try it for yourself.