A Klingon-occupied planet where color perception is blocked and the inhabitants live in a 1940s Earth style under constant surveillance.
Mat'aar XII is the main planet of the Klingon-occupied Mat'aar system in A Case of Chiaroscuro. Una Chin-Riley, Joseph M'Benga and Nyota Uhura hide there after recovering a missing Starfleet probe, and they find a world where color perception is blocked and residents dress like 1940s Earth.
The planet is ruled by the Klingon commander Kor, who oversees patrols and arrests while a resistance fights back. Posing as the resistance leader Nevette, Una completes a plan that lets some Mat'aarans escape.