I don't know why. Sometimes they just look darker. Maybe it has something to do with what they eat or the lighting? Maybe a bird expert out there can tell us.

The ones here are black with shiny irredescent blues & purpleish like the one here:
Found this too: LOL
Starlings know if you are watching them
May 1st, 2008 | weird
Starlings can tell if you are watching them, according to a study that has shown for the first time that starlings respond to a human’s gaze.
Starlings will keep away from their food dish if a human is looking at it. However, if the person is just as close, but their eyes are turned away, the birds resumed feeding earlier and consumed more food overall, according to experiments by Julia Carter and colleagues at the University of Bristol, reported today in the Proceedings of the Royal Society Biological Sciences.
Could this be exploited to make a better scarecrow? “Starlings do seem to have a reasonably strong aversion to eyes, even to artificial eyes, but these birds are also very quick learners,” she says.
“Previous studies have shown that starlings will learn within a matter of hours to ignore even relatively elaborate bird scarers – these devices never do what a real predator would, they don’t actually chase the birds or present any other signs of danger, so the birds quickly learn to ignore them.”