This will bring autumn/fall to all of Tamriel.
It is a very simple to use mod (though not simple to make), it has only two files (esp and bsa) and can easily be deactivated or deleted again.
And if you have them, you can switch with two clicks beween my other seasons, winter and spring and mabe even a tropical summer :)

This overhaul overwrites nothing.

I used only vanilla textures and meshes, with rocolores.

Winter: http://www.nexusmods.com/oblivion/mods/46618
Spring: http://www.nexusmods.com/oblivion/mods/46722
Tropical: http://www.nexusmods.com/oblivion/mods/46118
Summer: See original game ;)