English: Flag of the Sultanate of Delhi according to the Catalan Atlas (1375). The flag is grey with a black band in the Catalan Atlas (attached image), not green with a black band as previously uploaded.
The actual grey and black color appears clearly in the primary source (and the Catalan Atlas has plenty of green otherwise, so the grey cannot be a result of color fading), and this interpretation is confirmed by academic sources:

REFERENCE: "....that helps to identify yet another curious flag found in northern India – a brown or originally sliver flag with a vertical black line – as the flag of the Delhi Sultanate (602-962/1206-1555)." in (2010). "On the Timurid flag". Beiträge zur islamischen Kunst und Archäologie 2: 148.

WARNING: This is primary source image, the actual flag is otherwise unknown. The main source pointing to this design is the Catalan Atlas, which as a historical primary source. This image should not be added to articles without clearly attributing its primary source origin, and secondary sources are additionally desired if available (such as the one above). Note that FOTW (where most of those flags on Commons are adapted from) is based on user contributions like Wikipedia, and hence not authoritative.