Well by that thinking we'd have larger denominations of bills known as "Negroes". You can probably guess what they'd be called in common usage.
Given its Latin origins, the name Negro might logically be applied to a currency printed with a large amount of black ink. And the offensive slang word to which you refer would be butterflied out of usage as we remember it.
But back then, most money was defined by coinage, not bank notes.