red or black → ink

Evidence

"Fig. 42: Chapter heading in a copy of al-Muʿālajāt al-Buqrātīyah, executed in Marv, 611/1215 (OL 225). It can be written in red or overlined in red or black → ink."

Remarks

The image shows red headers and black text. In chronograms and headings, red ink or overlining in red or black was common practice (p. 58). This specific copy was executed in Marv in the 13th century. (p. 58)