Lower portion of sky no longer renders

The bug

The Overworld sky previously rendered on both the top and the bottom of the world, with the lower portion having a much more pronounced color. This lower half no longer appears to render at all.

Testing reveals that it stopped rendering in version 1.10-pre1. Reading archived changelogs for this version do not appear to list it among the changes, making its "removal" potentially accidental.

How to reproduce

1. Create a superflat world using "The Void" preset
2. Observe

Expected results

There would be an upper sky and a lower sky.

Actual results

There is only an upper sky in versions 1.10pre1 onwards.