The Colour Palette in Portal

The environment design of features 2 main colour schemes; the cold blues and whites of the test chambers:



And the warm oranges and browns of the secret hideouts:




The blues and whites reflect the sterile and impersonal nature of the test chambers, whereas the oranges and browns help to convey a more human element, that ties into the idea that these areas have been inhabited by people rather than machines. This colour palette is repeated throughout the game, with the blue and orange portals, for example.