Both species are in fresh non-breeding/winter plumage right now. The main distinguishing feature at a distance is really not the body spotting, it's the fresh fringing to the wing feathers, with Common Starling having very noticeable and broad pale (brown) and contrasting fringes to those feathers (wings stand out as unequivocally paler than the body at a distance), while Spotless has no such fringes and wings look uniform with the body.
Now the bird in the photo: is it just a black silhouette with no colour visible? Not at all.
It is dark, as expected given the species we're talking about, but plenty to see there: black "mask" on the lores to the eyes, reflections on upper cheeks, over the scapulars, upper breast (making a darker wing to almost stand out), and legs appear brownish (not black, as in a silhouette) which reinforces the idea that if paler fringes were present on the wing they'd be obviously visible. I don't see much problem with this.
P.S.: this could be useful:
http://blascozumeta.com/wp-content/...sseriformes/417a.identification-starlings.pdf