Aranjia

The Aranjia were a race of parasites, weakened by and fearful of the colour blue (cyanophobic). They tried to conquer planets like Thelka via wormhole. On Thelka they managed to take over the bodies of the rulers and all but eradicate the colour blue from the planet, including the skies, using a converted weather control system that filtered the colour blue from the sky – until the Doctor and Amy Pond modified the equipment and returned it to its former state. The Aranjia were driven back through the wormhole, unable to return to Thelka. (DWA: Blue Skies Thinking)