Urban camouflage doesn't mean blending in with buildings. It means blending in with people. If you want to be camouflaged in an urban setting, you don't use the same tactics as for jungle or desert camouflage, where you try to blend into the background. You should try to look like people who belong there. Boring people not worth a second look.
Mokalus of Borg
PS - That's how real ninjas did it.
PPS - Apparently.