Awful render color banding in Blender Internal using color ramp world texture

I am preparing to render an animation, and I am experiencing horizontal banding of color transitions on a background generated in Blender Internal using a world texture created with a color ramp:

The render generates horizontal banding as shown here, highlighted by brown dashed lines:

Earlier versions of the scene used a purer color selection… more in the deep-sea cobalt ranges, and I either did not see banding or there was none…?

Other settings that may be of interest:

Gaussian anti-aliasing on with 16 samples… and I have tried 11 and 8. It is present when no antialiasing is used, as well. And, for what it is worth, turning mist off decreases the problem, but does not eliminate it…

All input welcome!

To reduce banding you can add some dither to the rendered result (Render / Post Processing)