low-key

[ loh-kee ]

/ ˈloʊˈki /

of reduced intensity; restrained; understated.

(of a photograph) having chiefly dark tones, usually with little tonal contrast (distinguished from high-key).

to make or attempt to make low-key: to low-key the arms buildup.

Origin of low-key

First recorded in 1890–95

Later that night, this low-key man went out on stage with otherworldly energy.

When I Met Robin Williams in Afghanistan |Matthew Kaminski |August 20, 2014 |DAILY BEAST
In person, Ligety is fairly humble, and low-key—almost enigmatic.

The Can't-Miss Sochi Showdown: Bode Miller And Ted Ligety |Jake Bright |February 9, 2014 |DAILY BEAST
This is where having a low-key character like Deborah Samson, rather than, say, George Washington, was really helpful.

The Cross-Dressing Revolutionary: Alex Myers’ New Novel |Eric Herschthal |February 4, 2014 |DAILY BEAST
Instead, the star will celebrate tonight with a low-key dinner at home.

Justin Bieber Faces Deportation; NBC Moves Emmy Awards to Monday |Culture Team |January 29, 2014 |DAILY BEAST

Besides, her position dictated a discreet, low-key approach.

How Queen Victoria's Affection For John Brown Sprang From His Contact With Dead Albert's Shade |Tom Sykes |June 13, 2013 |DAILY BEAST
She dressed well, and low-key, and you could tell how smart she was just by looking at her.

Little Brother |Cory Doctorow

low-key

having a low intensity or tone

restrained, subdued, or understated

(of a photograph, painting, etc) having a predominance of dark grey tones or dark colours with few highlights Compare high-key