Indigo

 Dr. Indigo is a doctor who serves under Shiki. He is the one that created Boss and the other monstrous animals under Shiki's dominion.

Appearance
Indigo is an indigo haired doctor with a mime-like appearance. He wears a large yellow polka dotted indigo scarf and indigo-striped shoes that make a farting noise every time he takes a step. He also wears indigo overalls and a lab coat over them.

Personality
Indigo is a doctor with an eccentric personality. Like many characters in One Piece he has a distinct laugh and adorns shoes that emit sounds of flatulence whenever walking.

Shiki
Indigo shares a rather humorous relationship with his captain Shiki. Whenever Shiki says or does something stupid, Indigo acts as a straight man and slaps him. After which they both present themselves to others like a typical comedy duo after a joke. Regardless, he is loyal to Shiki and spent twenty years creating super-powered creatures in Merveille for the Golden Lion Pirates to take over the world.

Abilities and Powers
Indigo is a chemist of sorts. He was the one in charge in the development of Shiki's scheme involving all the monstrous animals. He may be a strong fighter who uses scientific materials since he was seen along Shiki and his crew when they fought against Gol D. Roger and his crew.

He appears to have an ability to produce explosive chemicals from his body and attack with them, it is unknown if it is the ability of a Devil Fruit or the effect of some chemical he uses in battle (since he used some chemicals in the battle with Roger 20 years ago), he uses his ability to create chemical orbs and arrange them above him and shoot them from his hand, and create a large orb with a much more explosive effect. He may also have some skill with a sword as he was seen attacking Luffy with it in one scene but it was never seen again.

Trivia

 * Of Shiki's main crew members, they all have a color in their name.