My main goal when I present images is to direct the viewer’s attention to the most important areas. The basic method of viewer manipulation is to change contrast. My first instinct is to use black & white (B&W). Color usually distracts the eye and B&W is easier to control by changing the relative tonality of elements in post processing.
Sometimes, color gives me the best result. In a few instances I almost desaturate the image, leaving some colors to accentuate details or to slightly preserve the unusual quality of light.
For anything that I do in photography, my choice between B&W vs. Color is based on what I would like to present. I never decide based on the notion of what is considered appropriate. Tradition should not set rules or precedent that dictates your freedom in street photography. Always exercise personal judgment when it comes to selecting between B&W vs. color.
In any case I always shoot in color (using RAW format) and there is absolutely no reason to do otherwise. I will talk about that further in a discussion about post processing.