Intuitive guess: The extract is excess Kakishibu (Persimmon) dye.


From a site listing some Kakishibu Cotton for sale:

"Kakishibu is traditional Japanese persimmon dye. Highly regarded and collected in Japan and across the world. This cotton was hand dyed by an artisan in Kyoto. I was lucky enough to find a large batch from the same artisan. Botanical persimmon dye reinforces the fabric and provides a water resistant coating. Thick like denim, this cotton is highly durable. Two edges have a smooth selvedge and two have been cut and sewn in."