He acted as a 'foil for' the comedian. [=he acted very serious to make the comedian seem funnier]
His reserved manner was a perfect 'foil for/to' her bubbly personality.
That dark blue dress is good 'foil for' her blonde hair.
(..) Is the US providing experimental military arms to rebels in Africa? You know with balls like yours. You belong in here. Who's your source on this? A tin foil hat? No, not tin, but it's metal. Fired in the Superman incident. Experts at the Pentagon can't ID it. - We haven't been told the truth. (..)2016 Batman v Superman: Dawn of Justice