expression, suru verb (irregular)
blacken; make black
Transitive phrase meaning to cause something to become black, either literally or figuratively (e.g., darkening an image, tarnishing a reputation).
写真を黒くするには、コントラストを上げてください。
To make the photo darker, increase the contrast.
彼はうわさで私の評判
He blackened my reputation with rumors.