A commenter on this image asked about the "blue" sky in my synthesized image, composed of UV, green, and near-IR frames. Color was suspect, but it's all I had at the time.
I took much more recent data from a few days ago (sol 1321) and used subframes that were actually blue, green, and red. With equal strengths you get the image above. The sky is essentially overexposed.
Without further investigation I'd guess the gradient across the frame is from dust accumulation on the camera lens.