Gradient
The Gradient option offers up to eight colors and works in two main modes:
Style - Lines
This is the default mode, which creates a gradient with horizontal color bands. The color bands are all parallel to the horizon and mapped onto a giant sphere. This means that when the camera is pointed up, more and more of the spherical shape will be seen: an increasing curvature of the color bands. To remove this curvature, open the Orientation and Distort group and set the Straighten control to 100.
Style - Points
This mode creates gradients that are controlled by up to eight longitude/latitude points on the giant sphere.
Eight color selectors are activated according to the Colors setting. They all have the same properties:

Color - The color itself. This value is keyframeable and can be overbright with value greater than 1.0 when the effect is used in 32-bit-per-channel projects.
Opacity - This simply sets the opacity of the color.
V Angle - The vertical angle (Height/Latitude).
H Angle - The horizontal angle (Longitude). Only active in the Style - Points mode.
The Gradient is active as long as an Image Map is not selected.