What’s with the red and blue street numbers in Florence?

There are two sets of street numbers, red and black (or blue).  Generally, all the red numbers are for business and merchants. Black numbers are for residences. Walking down a street in Florence you may see an 80 black next to a 132 red. So be sure to pay attention to which colour you are looking for.  You will often see an address for a store listed as 11 r, which means that the number 11 is painted in red, or rosso.