3.11.1  The Background

The background feature is used to assign a color to all rays that don't hit any object. This is done in the following way.

  camera {
    location <0, 0, -10>
    look_at <0, 0, 0>
  }
  background { color rgb <0.2, 0.2, 0.3> }
  sphere {
    0, 1
    pigment { color rgb <0.8, 0.5, 0.2> }
  }

The background color will be visible if a sky sphere is used and if some translucency remains after all sky sphere pigment layers are processed.