Plant that changes colour based on biome colour?

Duplicate the block.  Change it's texture to the one desired for a specific biome.  Add a procedure where if your bush is in the provided biome, replace it with the special biome version.  Make sure the new one is not in the creative inventory, and when you pick block it gives you the default bush.  Repeat this for all the biomes you want.  

I'm saying you will have to make all the variations a new seperate block to work, basically tricking the player to thinking they are all one block.  

the way that I would do the same thing is how plyonuclear said, make a bunch of different colored plants for each biome, pain in the butt, but I do the same thing with some of my stuff, multiple copies of the same plant or block for different kind of spawn pattern but they all drop the main item or block and copies not in creative, and the recipes use the main item or block.

it is a pain, but the end result will be worth it, and like how my stuff goes, by the time you get done adding them all and doing the procedures, you figure out how to do something else and you end up making more cool stuff, that you wouldn't have if you didn't go through all the pain.. :)