Spinner, the option in Picasa that you're using here is kind of like an extremely simplified version of selective colorization. It's not too difficult to get a far more precise look using the program GIMP (also free, and open source, to boot!)

If you'd like to learn it, here's a tutorial: http://www.gimp.org/tutorials/Selective_Color/

Here's a few pictures I did up using GIMP and selective colorization: