The grey notes thing when you fail is completely retarded and has no reason to be, please remove it or make it a toggle, it's a feature that is, in the best possible scenario, not annoying, and in any other, annoying, no pros whatsoever. We usually just add no fail to MP rooms so even if we fail there is no need to play with those stupid all-grey hit circles.
Some maps become unplayable with this (if you're not using visual settings) because of BIG BIG YEAH IT'S ALL GREY BG SB HIT COLORS BURSTS EVERYTHING and if you play on low gamma it may even be harder to play because grey circles can be a little hard to see on black BG. Even some patterns where new combos are helpful for reading become harder for no reason since you get all grey clusterfuck.
Really this is one of those features that makes me wonder what was peppy (or whoever thought of this) thinking when they implemented it.