And I realized that fog lets you see in terms of values. With colors muted by the fog, and the shapes of things accentuated (or muted), it's a great time to see things in a painterly manner. You can clearly see that the closer trees or objects are the darkest, and have the most color and distinction. The trees in the background are indistinct, just vague shapes, with the branches at the skyline the most defined.
This isn't a great photograph for illustrating what I saw today. It lacks the clear distinction of near through far. But you can see how the close trees (the tallest) are most defined at the skyline. When I take a better example, I'll post it.