This string is called Kirschbaum Gut Feeling (haha). I think this is probably the string Paul Coll plays with.
Paul mentions here that he plays with “Kirschbaum natural gut”. Kirschbaum do have a Natural Gut string but I’m guessing Paul uses the “Gut Feeling” string in Natural color. StringJob.nl says he uses the 17 gauge version.
Thanks B, M, and Tjeerd for the tips.