Here's what happened:
I played the game for PC.
I installed mods.
They didn't work.
Someone told me that shivering isles gives you the update you need to get the mods to work.
I got shivering isles.
I booted the game and "YAY!" the mods worked...there was only one small problem:
THE ENTIRE GROUND IS A RAINBOW! I turned off all the mods but still when I double click on shiverings isles to launch the game with mods the ground's textures are some weird rainbow! What is this madness and how can I fix it?! Right now I'm desperately trying to uninstall and reinstall the game and will install the mods slowly one by one...but does anyone have any advice?

What mods did you install?

i DON'T know about the small ones but some big ones include Quarl's texture pack, Natural environments, all natural, and such...I think it may be quarl's pack because everywhere there should be a quarl texture there's a rainbow. I uninstalled and reinstalled it and it's still there!!!!!

It's alright it's a role playing game just pretend your character has a skooma addiction and these are the unfortunate side effects

Sounds to me like your shaders are broken or that the game failed to patch them when it applied the update.

http://www.tesnexus.com/downloads/file.php?id=20348.

Ah thank you! For the time being I have got the shivering isles version of the game to be up and running without purple grounds. I hope it'll stay this way. Only thing left is...is it a mod that corrupted my game's shaders? Or was it the shivering isles...strange. Thanks anyways.

The patch likely didn't apply itself to the shaders correctly. That can happen sometimes.

Usually it's best to install all the official stuff before installing mods. You installed the game, then mods, and then installed SI. Installing SI may have overwrote some mod content (or rather official content that the mods change and then SI changed). I forget the details, but sounds like the problem you into may have something to do with what's called "archive invalidation" (http://cs.elderscrolls.com/constwiki/index.php/Oblivion_Mods_FAQ#Archive_Invalidation).

That's not how Archive Invalidation works. Oblivion has all its resources packaged into BSA archives, which help to ensure no vanilla resources get overwritten by modders adding in replacers. This also means that installing Oblivion, SI, or the patch will NEVER overwrite anything added by mods, because mods never alter those archives.

Archive invalidation only apples to resources that are loaded loose (that is, not packed in a BSA) that are timestamped to a later date than the BSAs. If both those conditions are met, the game will use that resource instead of the matching one out of the archive.

Archive Invalidation has no bearing on a botched shader installation.

However, your point is a sound one. Best not to install mods until after you've installed all the official content.