It all depends on where we're talking about...

The Professor was pretty forthcoming when it came to explaining just how bright and vibrant things were in the Shire, equally as vibrant in Rivendell. When we start directly discussing the events that take place in LOTR itself, however, we start to see more to the effect of the spread of Evil.

Color and vibrancy were allegory to the Free People, and effectively all good, where-as dull, dreary colors were meant more towards the Evil side.