1. Black plays only on the dark squares
2. Blacks dark square strategy succeeds
When one side is strong, and aims to play largely on the dark square colour complex, they are said to be using a dark square strategy.
In position 1 (Burrows - Williamson, 2008 [analysis]), black has purposefully given up his light square bishop in order to both make his dark square bishop stronger and to play against the pawn on b2.
In position 2 (Nakamura - Radjabov, 2011), black, having held on to a pawn on d4, could afford to give it up to achieve a dark square blockade and a drawn position.
See: 'Colour complex' and 'Light square strategy'.