What I've noticed about pigeons is that it's not a Good Thing to stand directly under a bunch of them...

Seriously though, in some places there seems to be a greater proportion of dark feathered ones than light feathered ones. For instance in Japan, you hardly get to see any of the latter. There was a TV program once showing that this was an adaptation to crows preying on the lighter ones; the darker feathers probably made the pigeons less likely to stand out.