You are probably right. He wears sunglasses for cool look. He is celebrated rapper in America as you know, for them, unique style is so important.
And he does success with the unique style. If he doesn't wear sunglasses, people wouldn't like him so much.
But, I still heard that he is so high in every second, so he needs sunglasses to cover his eyes in case that people think that he is a crackhead. No matter what, I like him with the sunglasses all the time.
Ok, from what you said, I can see that you just want to know the reason why that black singer always wears a pair of good sunglasses, especially when he was during a show or something. So, it is true that for those singers, sunglasses could make them appear to be awsome and more mysterious. Also, maybe that is just their habits. Meantime, some sunglasses could even protect their privacy and protect their eyes from harmful lights.