The word "most fluorescent" suggests a bright, vibrant quality that stands out. The antonyms for this word convey the opposite meaning, such as dull, dark, and muted. Some other antonyms for fluorescent include somber, gloomy, and shadowy. When used in the context of color, the antonyms could include grayscale, monochrome, or achromatic. These antonyms may be used to describe a space or an area that is not meant to draw attention, such as a funeral home or a museum exhibit with darker lighting. Alternatively, they may be used in a poetic sense to convey a different mood or feeling.