I have to say that there are no "black eyes", just dark brown eyes accentuated by various tones of skin to look like they are black. And sine you didn't have a deep research or let me say the observation on the so called black eyes, actually, and then are not black at all. The difference can be subtle or distinctive depending on the eye-colour. "Brown" can range from light, pale brown to deep, dark brown, which can be easily mistaken for black. Examples would be Asian. Asian have typically very dark brown eyes. Just go with your instincts. There is no officially correct answer as to which colour people's eyes are.
And if you want have the real dark eyes, you can were contact lenses with the color of dark. That is pure dark, and by the way, you can compare it to the natural so called black eyes, then you can see the difference by yourself.