Autumn Army - Shinobi Rat

"Ninja is the on'yomi reading of the two kanji 忍者 used to write shinobi-no-mono ( 忍の者 )... The underlying connotation of shinobi ( 忍 ) means "to steal away" and—by extension—"to forbear", hence its association with stealth and invisibility. Mono ( 者, likewise pronounced sha or ja ) means a "person".

"There is no evidence historical ninja wore all-black suits...
The stereotypical ninja who wears easily identifiable black outfits (shinobi shozoku) comes from the kabuki theater. Prop handlers dress in black to move props around the stage. The audience sees the prop handlers but pretend they are invisible. Building on suspension of disbelief, ninja characters came to be portrayed in the theatre as wearing similar all-black suits. This made the audience unable to tell a ninja character from the prop handlers until the ninja character distinguished himself from the other stagehands with a scripted attack or assassination."

cited from Wikipedia.