This is the Rue Crémieux, an extremely photogrnic and colorful street that attracts many tourists (too many, according to the street’s residents). It is to Paris what Lombard Street is to San Francisco. There’s even a sign at the entrance to the street asking tourists to not disturb the peace.
This photo doesn’t really do it justice, because of the time of day (around 4 PM). The houses are actually quite brightly colored.