Why is kraft paper called black paper?

Name it by color. The colors of kraft paper are as follows:

1, one is natural kraft paper, which is generally brown on both sides.

2, a double-sided white, double-sided white exactly the same, all white is generally called white kraft paper, white kraft paper.

3. One is white and the other is yellow. This kind of paper is generally called coated kraft paper or white kraft paper.

4. One is that both sides are yellow, that is, both sides are the same yellow, such as American cardboard and Russian cardboard.

5. One is single-sided kraft paper, that is, kraft paper has different colors on both sides, one side is carton color and the other side is white.

6. One is kraft paper with the same color on both sides, also called double-sided kraft paper, with the same color on both sides.

7. There is also black kraft paper, also called black cardboard, which is divided into single-sided black and double-sided black.