So I come out from closing an oblivion gate, and all the sudden, all the skies are purple. What's the deal with that? I searched the forum but couldn't find another topic on this, so I'm asking if anyone's had this problem and how it can be fixed. I'm not using any mods that change the textures of the skies.

My guess is you have one or more environmental mods conflicting with each other, and it's also messing with Oblivion's core programming. The graphics for the sky effect around Oblivion Gates are a part of the Main Program. I would suggest you deactivate your environmental mods one at a time to discover which one is glitching your game.

Or perhaps you deleted some files after cleaning up a mod you no longer wanted, and accidentally deleted an original game file.