There will be 3 Black Bulthaup Tigers sailing the dutch waters this season. Very beautifull boats.
I think the paint is put on the sails similar to my sails.
something like graffiti. There's no disturbance of the airflow because of the very thin paint layer on the sailsurface. The weight is also minimal, especially compared to have it covered with black stickers.
The paint weighes approx 100 grams.

I added a pic of my Tiger.