What colored the tissue?

Videos on You Tube, the seven part Fairy Tales Live Restoration. Part 7, addresses using a bit of Japanese tissue to help “repair” a previously colored corner. At approximately 13:17 into that video, a piece of dark brown paper is used. Was that paper purchased that color or was it colored after purchase? If purchased that color, what was the source? If colored after purchase, what was used – both paper and coloring substance? Thank you.