Used as a noun or na-adjective for dark colors, atmospheres, themes, or moods. Common in compounds like ダークスーツ (dark suit) or ダークな雰囲気 (dark atmosphere).
This movie's dark atmosphere is its appeal.
He prefers dark-colored clothes.
That movie has a dark atmosphere.
Choosing dark-toned clothes gives a calm impression.
ブラック names the actual color black, whereas ダーク describes deep or muted shades of any color as well as gloomy themes, so they overlap but aren't identical.
dark matter
dark horse
dark web
dark elf
dark gray; dark grey
dark side
dark store; online-only retail outlet
dark suit
darknet; dark net
Loanword from English 'dark'.
dark blue
dark pool; dark liquidity
after-dark clothing; evening wear
dark green