ground colors and angles - ground gradation

sky colors and angles - sky gradation

more . . .

Background {
    groundColor [ 0.0 0.2 0.7, . . . ]
    groundAngle [ 1.309, 1.571 ]
    skyColor    [ 0.1 0.1 0.0, . . . ]
    skyAngle    [ 1.309, 1.571 ]
}