One who contrasts; a person or thing that creates, shows, or emphasizes contrast.
From 'contrast' plus the agent suffix '-er' (one who does something). A rare noun form creating an actor or agent noun from the verb 'to contrast.'
In Baroque art, light itself becomes the 'contraster'—it's the element that creates the dramatic visual contrast that defines the entire style and makes viewers' eyes move around the composition.
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