Minecraft wiki entry for Color, associated text: The world border in Java Edition has several colors. A blue color is applied if the border is stationary. If expanding, the world border takes on a green hue. If the world border is shrinking, the world border turns red. In the Nether, the world border is always red no matter if it is expanding, stationary, or shrinking. The world border becomes more opaque the closer the player is to it, and more transparent if the player is further away.