Light up sky above horizon when Sun is up

[patudom]

This is a request that would also apply to the desktop client, but I would prioritize its implementation in the web client and web engine first. A lot of teachers would like students to be able to explore what constellations can be seen at different times of year from different parts of Earth. In addition to #318, it would be very helpful if the sky above the horizon could be shaded light blue during the day, to signify that the Sun is up in the sky. (It doesn't feel like "daytime" if you can still see all the stars against a dark background).

Even if it's done in a hacky, not-beautiful way, this feature would be much appreciated in the education community.

[pkgw]

Gotcha. As ever, our engineering bandwidth is limited, so please ping here if this starts rising in urgency for you.