Sorry, LaFoto--didn't mean to be cryptic. This was shot in fairly late afternoon. If you shoot a blue sky with a polarizing filter and convert with the channel mixer, this is about what you get. Boosting the red channel makes the sky even darker. Trees with white bark, such as sycamores and cottonwoods in my area, stand out nicely against the dark background. I had this approach in mind when I took the shot.
Myopia, thanks for the feedback. The tint is pseudo-selenium, done with a color curve. I like it but tastes vary.
I would have guessed infrared if I hadn't read the rest of the thread first (and also, the rocks break that theory).
The tint for me makes the image feel very stark -- not warm at all. These feel like winter trees, and the winter may not end. That's a pretty definite emotion, so that's good.
However, I also feel like the branches lack clarity or sharpness, which would help the starkness. If they were extremely sharp against the sky, that would increase the feeling that this is a very cold winter day.
Then again, maybe I'm reading something totally different into this than anyone else.