I was finally able to figure out how to add a subset to an object and how to make it recolorable, and my journeyman's piece is the Sims 3 neighborhood billlboard from the basegame that I resized to half its size and made available in buy mode under 'Sculptures'.
It's not as grungy looking as the urban billboards from the 'Late Night' expansion pack that I made earlier, and it has a rather shiny surface as it is cloned from the 'Apple of the Eye' statue, so it would probably be better placed in the posher areas of your town.
If I can bring myself to work on a second version of the billboards, I'll do a more grungy looking one. :-)
Download here:
http://www.mediafire.com/?efuaj7lbypwpg6b