How would you go with painting a simple blue sky as a background?
A few different ways you can do this, like drawing a skybox or even a blue quad.
The simplest however is probably just clearing the background with the color you want.
GL11.glClearColor(0f, 0f, 1f, 1f);
GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT );