Sunset sky. Strong saturation probably would have ruined the delicate gradient of the sky. One of the rare cases it really matters when choosing the compression quality settings. My first attempt had some noticeable banding artefacts. When reviewing this picture on the computer, I noticed the faint halo around the sun, visible in the upper middle part of the image. The aero plane is in a more blueish part, between the halo and the sun itself. The sky seemed absolutely clear so I wonder what that can be.