Street photography, or as it is alternatively known, urban photography, is a branch of realistic fine-art photography. It mainly features human conditions in public places in urban environments. Street photography takes records of the human scene in streets, restaurants, stores, libraries, parks, airports, trains, museums, buses, among other places. It records daily human activities such as reading, playing, shopping, sitting, standing, eating, and partying among others. In addition, street photography also includes records of objects or environment that projects a human character in an aesthetic and facsimile manner.
The above is the definition of Street Photography to which I subscribe
Street photography is one of the hardest and most fast-paced genres, leaving little to no time for the composition, which is why a street photographer is always ready to record with his camera the instant that a fleeting moment occurs, before it is lost in time forever. Whilst studio photographers can often take all the time they want to create their image very carefully, street photographers have to react on the street very quickly.
Contrary to the primary focus of most photographs, street photographs are not concerned with the artistic effect of the photo, for example, a documentary photograph that puts more emphasis on the content of the picture. And in street photography, you expect to see both sharp and blurred impressionistic image, both acceptable for this genre.
Why does most street photography appear in B&W? Well I can't speak for anyone else but personally I see mostly in tones, as I'm colourblind! Though strangely enough, I can see 'colour' in a black and white image!