A Challenge for Bird Lovers

Katerina has a bird in a cage that she says was originally wild. She says he was a baby when she first got him this Spring and it’s a male, so obviously the sexes of his species are different. I can’t find anything even similar to him in my “Birds of Europe” book, and I’ve searched carefully, twice. Can you identify the mystery bird from the following description?

He’s smaller than a sparrow, with a long, slender build. His feet are for perching (not webbed). His legs are not unusually long, so he isn’t a wader. His beak is straight and slender, needle-like. It isn’t long or heavy, like a woodpecker’s, nor hooked like a parakeet’s, nor triangular, like a sparrow’s, and (I won’t swear to this, but I think) it’s dark. He is mostly black, or at least very dark, with white or light underparts. He has black cheeks, the black curving down along either side of his throat, but the throat itself is white. (Yes, definitely.) He has a small, distinctly rust-red dot on each cheek, like a cockatiel. He has one or two bright yellow feathers in his otherwise dark tail. He carries his tail down, not cocked like a wren. The light in which I was observing him wasn’t the best, but I couldn’t see any speckles or bars on his breast at all; it appeared solid white. He has no crest, or perhaps I imagined the merest hint of one, nothing prominent like a cardinal’s. He has a pretty, melodious voice. He is very active, nervous, and not fond of his cage. He eats seeds, in captivity at least. I watched him tuck eagerly into a fresh cabbage leaf, too.

That’s it, but you should note I’ve probably missed something important, like wing patches I didn’t notice, or whatever. I thought I’d observed enough to distinguish him easily enough, so I didn’t pay attention to everything you would have.

Anybody?