When it comes to choosing sunglasses, you should think about our skin tone. Your dark skin tone belongs to cool skin color. For people who have cool skin tone like you, frames in blue-based hues are recommended. For example, blue, black, tortoise eyeglasses frames will look good on you. Hope this helps.
Typically, sunglasses color will take into account when you choose the sunglasses. Maybe the ability to meet the needs and reducing the ultraviolet is most important. Experientially dark gray is better, followed by dark brown, black, blue and purple. If you have a dark skin, maybe the deep purple is ok. In addition, the deep purple is a popular color this year. Your skin is a little black, but you wear dark purple glasses will make you glow with the unique charm.
You said you have a dark skin, so I do not recommend you to buy a pair of dark sunglasses. The dark color will make you look worse. You can try white-colored frame with brown-colored lenses. This kind of sunglasses I advise to you can make your face brighter and also can catch many attentions. Except considering the color, you also need choose glasses with suitable shape upon the shape of your face. I advise you to go to eye store and find the best sunglasses for yourself after trying.
When selecting a pair of glasses, most people know to choose a pair that matches their face shape. Face shape is only the first thing to consider, though. After you've determined your face shape and the style that best suits you, it's time to consider another important factor in selecting a frame: skin tone. If you think that's being too picky, you're underestimating the power of color. Glasses are worn on your face and because of this, matching them to your skin tone is essential for anyone who is serious about fashion. For your situation, you'd better select lighter shades of sunglasses, such as brown and matte black. Do not get stunning green lens because they will make you even darker. So, black rims or gold will match your skin color best.