Pirates in the Golden Age of Piracy acquired and disposed of ships of all sizes with frequency. Far from shipyards and supplies they maintained them as best they could, so the answer most likely is they looked like poorly maintained versions of whatever type and flag of ship they began life as. The following description, from the excellent Republic of Pirates by Colin Woodward, I'd imagine was typical of most pirate ships plying the Spanish Main.

Williams kept the Tanner's topmast because at this point the Marianne was in rough shape. The pirates had been in possession of the fifty-ton sloop for nearly a year, during which time they had weathered storms, fought at least one serious battle, and captured nearly fifty vessels. They kept her bottom clean, as best they could, by careening regularly and keeping the areas below the waterline covered in white lead paint. As pirates, however, they had had no access to proper shipyards or port facilities. Above the waterline, the Marianne was becoming a wreck. The yellow and blue trim decorating her quarterdeck was peeling, as was the blue paint on her stern. Her single mast had broken just above the deck, a critical wound that had been shored up by lashing on an old spar against it like a splint on a broken leg. Her sails were old and covered in patches. The old English flag, the red cross of St. George, fluttered from her bowsprit, under which a large chunk of the upper part of the bow was missing. Williams could further reinforce his injured rigging with the Tanner's topmast, but pretty soon he would need to get the Marianne a new one.

[Edit: Source, as footnoted in Republic of Pirates.

Condition, description of Marianne (c. April 1717):

C05/1318, No. 16iii: Deposition of John Lucas before John Hart, Annapolis, MD: 13 April 1717; C05/1318, No. 16iv: Deposition of Joseph Jacob before John Hart, Annapolis, MD: 13 April 1717.]