Red and black street numbers/addresses in Florence

Finding an address in Florence can be confusing. It has a unique address system with two number systems running side by side. Generally speaking, residences have a number in black or blue, while businesses have numbers in red (rosso in Italian), which is usually written with a little 'r' following the number. This gets confusing not only when the same number appears twice on the street (in red or in black) but also when you are trying to find an address and the door numbers appear mixed up.

For example, the office address of Walkabout is Via dei Neri, 30/32r (red) to signify a business and it is next door to number 6 (in blue on a white background), which is a residence.