Before the Timeskip
As a direct result of the modifications that he conducted upon himself as well as years having spent as a ship dismantler, bounty hunter, and street thug in Water 7, Franky is a powerfully built man with a height of at least seven feet, making him the second-tallest member of the Straw Hat crew. His forearms are relatively enormous while his biceps are comparably small. He has brightly-colored blue hair and blue star tattoos on his forearms. His choice of clothing usually comprises of a speedo, which causes people to call him a pervert, and an open loud Hawaiian "Aloha" shirt with a large golden chain necklace around his neck.
During his first appearance in the Water 7 Arc, Franky wore a masked costume as a disguise. But after discarding this disguise, for the rest of the arc all the way up to the end of the Post-Enies Lobby Arc, he wore a red Hawaiian shirt, with lime green palm trees decorating it.
During the Thriller Bark Arc, Franky wore a yellow shirt with purple trident-like symbols on the sides and a large one on back.
Near the end of the previous arc all the way up to the Sabaody Archipelago Arc, Franky switched to wearing a purple verison of his Hawaiian shirt.
During the Straw Hats separation, Franky wore a red coat to protect himself from the cold while on Barujimoa, But after blowing up Vegapunk's laboratory, the skin on his face was burned off, revealing his exoskeletion underneath. Which he covered up with a tiger skin rug.
He also has a pair of sunglasses which he usually wears when things start to get serious.
After the Timeskip
Franky is first shown to have a hair in the style of a buzz cut, and later on, he reveals that his hair is now controllable and can change different styles instantly by pushing down on his nose for more than three seconds.
He also has two stitch-mark scars on his torso running down from the back of his neck indicating that he had sewn his skin back on, making it seem more than likely that he has finally fashioned his metal endoskeleton to wrap around his entire body, and not just his visible front (since the initial operation to become BF-36 was done by himself, he could not do work on his own backside).
His shoulders, torso, and arms are also much bigger than before, and with studded hands that look almost robotic in appearance, but he also revealed that inside of his huge arms he still has a set of normal-sized robotic hands. He now appears to be wearing metal rigged suspenders. He has replaced his elbows with large, light blue hinges, his shoulders with a large red ball and socket joint with "BF-37" written on them, and his forearms with large, light blue cubes, with his trademark star retattooed being split by an edge.
These new features house upgrades he gave himself during the last two years, but their true potential and ability has yet to be fully shown.
He now wears a red coconut tree-motived Hawaiian shirt and red speedos. After all these modifications to himself, he is now currently the second tallest member of the crew.
While on Punk Hazard, he was given a large double-breasted black coat by Kin'emon, for the cold, using his unnamed Devil Fruit ability.