The fallacy of gray is a belief that because nothing is certain, everything is equally uncertain. One who commits this fallacy may reply to the statement that probability of winning a lottery is only one in a million by saying: "There's still a chance, right?"
This fallacy is invoked by those who wish to attack a well-performing system (e.g. Science), by saying that it is still imperfect. This then excuses the imperfections of the invoker's chosen system. For example "Science is based on faith too!"