Love it! The bright colours juxtaposed against the grey buildings just jumps out and smacks the viewer in the face. (As graffiti goes, it's rather attractive actually)
Very cool! Awesome select coloring choice. I am curious though... in the most upper right hand section of the photo it appears that you masked a section and filled it with a solid or near solid. What was behind that part of the wall. Maybe you didn't, but that part of the background seems to be a solid color. I'm not messing with your image, it's very cool. I'm just curious more than anything.
Actually just spotted that, it was in fact an all blue billboard, I simply used dodge and burn but with your sharp eye, you spotted a tiny bit I missed, thanks.