How does one decide if an image should be black and white or color? There are as many explanations as there are photographers to explain. For me, it's always intuitive. Color expands and stretches the imagination, tickles the brain and fires up emotions. Black and white subdues and reveals the structure, focuses the eyes and makes you think. Woodstock was tie dye but formal events are always black tie. Musicals are in technicolor, film noir is black and white. I suppose I tend to choose color or black and white based on the mood of the subject -- or my own mood when shooting the subject.
Sometimes, though, it's interesting to mix it up. Like here. The whimsical blue building above looks much more serious and austere in monochrome. It's kind of fun to move past the obvious and find another layer.