The term "most prismatic" refers to something that has a highly reflective and colorful quality, often seen in crystals or gemstones. Its antonyms would be words that describe the opposite qualities, such as dull, drab, and colorless. Other antonyms include cloudy, murky, and opaque, which suggest a lack of transparency and luminosity. Instead of being eye-catching and dazzling, objects that are the opposite of prismatic are often understated and unremarkable. So, if something is not considered most prismatic, it may lack the vibrancy and brilliance that make it visually appealing and striking.