Cobalt 17

The Azure Plains of the planet Cobalt 17 were a predominantly blue location.

After giving someone the task of drawing an arbitrary alien landscape around a picture of the Doctor's TARDIS, and then colouring it to match, the Thirteenth Doctor cited "park[ing] [the TARDIS] on the Azure Plains of the planet Cobalt 17" as being against the rules of the game, as the point was for the Doctor to get to see her box in a different coat of paint than the usual TARDIS blue. (NOTVALID: Colour Chameleon)