Colorfix settings:

Color saturation, red 0.9 (small values increase saturation!),
green 0.9, blue 1.0 (=no change).

Brightness/gamma:
Shadows and midtones 1.0 (=no change),
highlights 1.1 (lighter)

Sharpened (too much for on-screen viewing, but perhaps not enough for printing).
I also tried to remove noise from the sky (magic wand + median blur filter),
although the noise level was quite acceptable even without any processing.