*Do the normal LEVELS, CONTRAST, CURVES to your original pic
then desaturate your colour image (CTRL+SHIFT+U)
Then toggle the history brush in the HISTORY panel (use the help function to help you around)
start painting over the areas where you want to colours to show.
for non destructive post production, a suggestion would be to add a chanel mixer layer. this is to convert the pic in to bw. this is a layer mask and thus painting black onto the selected areas will mask out the effect of this layer, leaving behind the original colored background.
the advantage of this method is that you still have the original and everying you do is on layers... you can switch on and off varioius layers thus enabling you to see the various effects you have made in an instant.