Flashiest can be described as showy or flamboyant, so antonyms for this word would be subdued, modest, or simple. If something is not flashy, it may be understated or subtle. The opposite of the flashiest in terms of color can be described as muted, plain, or even drab. When describing fashion, the antonyms for flashy could include classic, elegant, or refined. In terms of behavior, flashy could be replaced with restrained, calm, or even conservative. Overall, antonyms for flashy can be anything that describes a lack of extravagance or excess.