'Black' in the Bible

Neither should you swear by your head, because you cannot make a single hair white or black.

When He opened the third seal, I heard the third living creature say, “Come!” And I looked, and there was a black horse. The horseman on it had a set of scales in his hand.

Then I saw Him open the sixth seal. A violent earthquake occurred; the sun turned black like sackcloth made of goat hair; the entire moon became like blood;