Ivona, I went back and looked at the strand I knotted with the MossGreen PowerPro last April (this post:
Stringing Pearls) They have been stored in a pile on top of my dresser* - not in direct sunlight, but exposed to daylight on a daily basis. The color appears completely unchanged from before. I would have no qualms about using it for your rope.
*my beading grade pearl necklaces I store in a bowl on top of my dresser because it is a luscious piratical look and it makes it that much easier for my niece to play with them whenever she comes over to visit...