"Hang out our banners on the outward walls; / The cry is still, 'They come'; our castle's strength / Will laugh a siege to scorn." —William Shakespeare, Macbeth
Lands you control are Plains. Nonland permanents you control are white. The same is true for spells you control and nonland cards you own that aren't on the battlefield. You may spend white mana as though it were mana of any color. You may spend other mana only as though it were colorless mana.
Icatia's once-peaceful towns faced increasing attacks from orcs and goblins as the climate cooled. By the time the empire fell, they were little more than armed camps.