Gene51 wrote:
If you shot them as raw, then all you need to do is adjust the hue, saturation and luminance for the color you are trying to fix. If you only have jpegs, then you may try a selection then a mask, to isolate the sky area, and you can do any number of things to it, but without seeing a sample image I cannot help you any further.
Even if you did not shoot in raw, in some programs (including PS and PSE) you can open a .jpg "open in camera raw". You likely won't be able to do as much with it as with an actual raw file, but it might help.