Thanks for that Madoc and the team. It's good to hear how life can be leant to the world. I think colour and aesthetics can be used to create distinctions/juxtapositions (although with some sense of awareness - for example if you look at that picture RichardTito posted as a "how not to do it" example, you wonder if whoever made that mod had ever walked through a forest before). There's still room for colours and distinctly man-made forms (although those latter tend to take care of themselves when you're designing a coaching inn or city), but I agree it needs to be done right.
On that score, you can refer to the 'There Will Be Blood' video: the addition of fire to an otherwise grey area, coupled with only one or two other light sources, leant the scene a more stygian feel, appropriate to battling an ogre in a catacomb. In a tavern with more wooden construction, better lighting and a few warm tones on people's clothing, that same effect would help create a sense of relative comfort and security.
Especially if you've just stumbled in from outside, having spent half the night running from hostile creatures...