In early episodes of the series, Paladin's trail clothes were a rich midnight blue. This nicely complimented Richard Boone's blue eyes--they registered as black on the black-and-white film of the day. There was a shirt redesign from a buttoned front to a V-neck and the colors of both changed to black around that time. Whenever Paladin's clothes were referred to in dialogue, he was always called "the man in black", whether he dressed in blue or black.
Regarding the name Paladin, it comes from early European "paladino", "palatine" referring to a knightly, heroic champion who fights for a noble cause. "Paladin" can also refer to a military leader; trusted and relied on by his king. Both the "knight" (a "warrior") and "military leader" speak to the character's--Paladin's--military background.
Parts of the first season-episode "The Colonel and the Lady" were filmed on sets used for the television series Gunsmoke (1955). The Long Branch Saloon is very minimally redecorated to stand in for a saloon Paladin visits in a Nevada mining town. Shots of people walking the streets of the town were also taken from "Gunsmoke".