These words are thought to derive from Dutch mot or Norwegian mutt and the biblically famous mote, all referring to small particles. From this, motley became multicolored, many disparate colors. This is the original meaning.
So motley fool, refers to the traditional fool/jester's multicolored costume. By analogy, motley may now be used for any disparate collection. In fashion, motley refers to multicolored dress, like patchwork.
... and three young women in motley and bells.Assassin's Apprentice by Robin Hobb