Ah, McStout!
I think it woudl be hard to extract the color without extracting the vegetable flavors as well. In Middle School we extracted the color from leaves by dipping in hot alcohol. I think... It was "a while" ago.
IIRC we placed alcohol in a double boiler and dipped the leaves in and it stripped the protective coating off the leaves and extracted the color. Of course you are getting a bunch of other things as well.