Upgraded Community Shaders, had way-too-bright foliage in the mornings and evenings. Found the culprit, "No Sunlight Through Mountains"

EDIT: as wankingSkeever points out below, the simple restart of the game might have fixed a transient issue. The shaders did rebuild before those screenshots were taken, and of course rebuilt again after I disabled NSTM. Now I can't say this is the cause until / unless someone else duplicates the outcome.

EDIT: The images were on postimg, and they've expired.