I would recommend trying one of the large amount of freeware sky texture add-ons. Perhaps someone here can recommend one or you can search on AVSIM. This can confirm that what you are seeing, and wanting changed, is the sky texture/color.
If that's it, ASCA does include quite a bit of content including sky color, and there are also many other payware and freeware add-ons as mentioned. Any of them can do this.