If you hear or see references to "black" metal, this is not about the skin pigment of the artists. It means "black" like scary, depressing, grim, angry, harsh, pessimistic. I came upon a sampler video of "black" metal bands based in Kenya, but one of the bands was all white guys. Most of the vocals, logically enough, were in African languages.
I am leaving that video unlinked: not because I heard any naughty words in it, but simply because the melodies indeed sounded VERY unhappy and angry. This does not prove all of the musicians to be wicked men. Black metal CAN be guilty of actually favoring evil, but this is not an invariable certainty. One group, in fact, was introduced as a Christian band.
Not all Christian singers are called by God to be nothing but happy-wappy all the time. They can inwardly rejoice in the Lord, yet be called in their public persona to "grieve with those who grieve"-- to empathize with souls who are too deeply wounded to be helped by a forced cheerfulness. Such souls will even be INSULTED by forced cheerfulness, because it refuses to take their pain seriously.