That's not quite Pavel's "Fantastic Knot," but it's similar. Daryl is the one who's popularized the trick in the US, and he includes his handling with it.
As the finale of the routine, a white knot jumps from a white rope to a red rope, and then you untie the knot and show that the white section of rope has actually become part of the red rope.
However, I would start the search with Pavel...he's got so many good visual rope tricks, it's probably one of those.
Aldo Columbini has a similar trick, look into his stuff too.