I was thinking about this today and I think it comes down for me to the following example: I can make a photo I'm happy with under constant lighting (under a cloudy sky for instance) that "works" in color. Imagine a collection of colors arranged together. It can work (for my eye at least) even though the light is constant. Such a photo would fail (again, for my eye) in black and white. Textures work, tonal variations work, and such. But I have an easier time with color as a thematic construct. Without the color, I produce nice stuff, sometimes good, but not often stuff I'm happy with because it's black and white, often it's good despite the fact that it's black and white.
Maybe it sounds silly, but I feel like I don't know how to make a descent photo in b&w under constant light.