"Pirate Lolita" is often considered a main sub-style of lolita fashion. Arguably because of the brand "Alice and the Pirates", and their year-round releases of tri-corn hats and treasure chest style handbags. However, "pirate" costumes are also a very popular mainstream halloween costume, so the overlap works as a halloween-lolita idea I think.
key aspects of Pirate outfits include: Eyepatches, tri-corn hats, chest shaped handbags, wide belts, lots of jewelery.
One of the best things about this style is total freedom in colour schemes. There are no specific colours associated with pirate lolita, so you can make it as sweet or as gothic as you like!