Now when you bring up the Levels tool, you will have better fine control of the gamma and black point. Be careful when adjusting the black point - remember, you are clipping data whenever you adjust it. Generally, it is not desirable to raise the black point so far that the sky background becomes completely black.

If your sky background still has a color cast, now is the time to remedy it, by adjusting the black point and/or gamma sliders carefully for the individual red, green and blue color channels.

This image is looking more and more like a final result. What's left to do in Photoshop are saturation and curve adjustments, and perhaps some noise reduction.