Hermit Purple manifests itself as multiple, purple, thorn-covered vines that spawn from Joseph's hands. The vines are strong enough to support his own weight and long enough to bind someone completely.
Hermit Purple is consistently portrayed as being purple across all media featuring it, befitting its name.
Hermit Purple's vines are relatively weak, but they provide Joseph with considerable divination ability, enabling him to divine and materialize any type of information, such as an image, a location or even thoughts.
Joseph demonstrated that he can use the vines as ropes, whose movements he can control at will. Their length and resistance make it possible for Joseph to swing from place to place[1] and tie someone.[2] The vines have limited resistance and a sufficiently strong Stand or even a strong Vampire can break them.[2]. The vines are dexterous enough to manipulate a video game controller.
Divination
Hermit Purple's main ability is to divine information. By using any object or material in conjunction with Hermit Purple, Joseph Joestar can display any information he wishes to see. To date, he has used Hermit Purple to:
Produce psychic photographs by destroying a camera.[3] The broken camera then produces a photograph which will reveal the information as it is in that moment of time, such as a person in their current situation.
Produce live psychic videos on a television.[4] It can either randomly display different TV channels to formulate a coherent sentence which will show a person's thought or film a place, even the most improbable ones such as the interior of Joseph's brain.
Analyze machinery to see if it has been tampered with in some way as he did with Telence T. D'Arby’s video game cartridges and console.
Conjure a map out of dust on an unpaved road, with precision on the location of a desired item.[5]
Ripple Transmission
Joseph has shown the ability to transmit the Ripple through Hermit Purple as an extension of his body. Joseph has used this property of Hermit Purple to attack DIO[2] or prevent him from touching him by wrapping himself in it.[6]
Trivia
Hermit Purple's thorns can briefly be seen in the background of the second opening of the JoJo TV anime, "Bloody Stream". This acts as foreshadowing, as the episodes that the second opening is attached to adapt Battle Tendency, and Joseph does not develop Hermit Purple until the following part, Stardust Crusaders.