I had a sky file called skynebula. It was the one that made it look like there were galaxies all over your sky. I got tired of it so I simply removed it..well now my sky looks like this.
(http://i57BannedImageSite/11uycz6.png)
I'm not sure how to get rid of the yellow stuff ;P I've looked through backup files and I have everything I need. So why did removing the skynebula image from my textures folder do this?
EDIT:: I fixed it. The picture had messed with the sky.mat so I simply had to replace that.
You'll want to try going into media > materials and open the one material file named "sky.mat." Replace everything that's in there with the following.
It turns that yellow and black because the game is wanting to find the texture that you took out I believe. Hopefully that will work for you. ^^