Originally posted by S.R.H.The background should be darker than the foreground; not vice-versa!
This should not be considered a "rule" of sorts. You must consider where the light source is located. For instance, Manuz mentioned the first room of Bowser's Castle. It was perfectly fine the way it was, because of the candles in the BG. They were the light source, and they were obviously closer to the BG than the FG, so it's logical the BG should be lighter than the FG in that case.
My suggestion to the author would be to add some sort of light source in the BG (candles, ghost house lamps), so it'd be technically right AND it'd still fit the chosen atmosphere (and even make it cooler :>). Dunno if it would be something beyond the limits of the "vanilla" style of this hack, though.
But tbh, it's not a big deal. Sometimes the small issues (those that don't affect the gameplay much) actually make a hack feel more unique and memorable.