Many things can influence how you process a photo or photos that you're working on. It may not even happen as you're working on a shot, but only after you've finished and think you're happy with an image. This blue bench caught my eye and I thought the pop of color was perfect; until I finished processing it.
I'd finished with the photo, had highlights and shadows where I wanted them, and the pop of color was how I envisioned it. Something happened though, and my mind focused only on a single word; "colored." My mind went back to thinking about the white supremacists march in Charlotteville and how so many minds are focused only on color, which made me see the photo in a different light and thought it would work better as black and white.
All of a sudden I felt that the photo had more weight to it, and when I shared the photo I also shared a bit on how I felt about the march and the mindsets. Sometimes a photo is black and white because it just works, sometimes not focusing strictly on color, is the message itself.