Okay so after seeing this I knew that this must happen in IC2.
Terraformer + Woolificator = Woolify your world!
Natural blocks would only get changed
From the 16 colours (Ores can be optional):
Red - Redstone Ore, Netherrack
Orange - Pumpkin, Copper Ore, lava *as pointed out below, this will be problematic. A solution is that all the lava is turned into a different block first then into wool*
Yellow - Sand, Sandstone, End Stone, Gold Ore
Lime - Grass, Uranium Ore, Reeds
Green - Leaves, Cactus
Cyan - Water
Light Blue - Diamond Ore, Ice
Blue - Lapis Ore
Brown - Dirt, Wood logs, Iron Ore, Soulsand
Light grey - Gravel, Mycelium, Clay
Grey - Smoothstone
Black - Obsidian, Coal
White - Snow (this may turn up a little wierd), Tin Ore, Birch wood logs (if possible)
I think I hit most of the natural stuff and suggestions/changes are welcome. But seriously this would be awesome/funny to have.
(Radius, EU cost, and recipe is whatever IC2 team feels it should be)