Opalescence

Opalescence, or Opal for short, is Rarity's cat.

Personality
She shares her owner's tastes in fashion and begrudgingly assists her with her work. Most of the time, however, she prefers to sleep on the various fabrics about the studio.

History
Opalescence is a white cat with a purple bow on top of her head. She wears a purple collar studded with opals. Although Rarity has expressed that Opal often swipes at her when she attempts to groom her, Rarity seems to have a deep caring for her cat - instantly forgetting her woes when she saw Opal apparently stuck in a tree.

Opal also seems to have a sarcastic sense of humor, chopping off some of Sweetie Belle's hair and offering a smug look afterwards when Sweetie Belle suggested she might be good with animals.

Trivia

 * Opal's squashed face and fluffy fur are similar to Persian cats, which are the most popular pure breed of cats.
 * When something is considered "Opalescent" it exhibits a play of colors like that of an opal or it bears a milky iridescence.
 * Whenever Opal is focused on throughout the show, her actions are accompanied by a brief harpsichord trill.
 * Opal has been sent to Fluttershy for a "grooming appointment" at least once in the series.
 * Opal might have a sense of fashion (like Rarity).