Sometimes it's never a good idea to answer your door without something to hold the door back in case a crazed blonde mare with a bound up heart for a cutie mark and her special talent is the art of the knot, barges in to your cottage with rope and a rag using her magic to bind you up before you have a change to react... This is a lesson that Fluttershy will never forget... if she escapes that is...

If you are wondering why Love Knot's magic is grey is because after talking to a few people, the magic glow for unicorns are determined by their eye color (Twilight's eyes are purple and his magic is purple, Rarity's eyes are light blue and her magic is blue, etc etc.)