Hi Larry, If there's an appropriate use for selective colour photos, I think this is it. In this case, I believe it really adds to the feel of the image, and in combination with the perspective, manages to really draw the viewers eyes to the graffiti. Very well done.
One small point of critique, I think if you had desaturated the coke can in the garbage too, the impact would've been even stronger. I think I see your point of keeping the red in the garbage bag too, making it a part of the theme, but to me, it's more of a distraction than an addition to the feel and atmosphere. The garbage bag itself is present enough even without the red. But that's just my opinion. Nice shot, and well post-processed.