I’ve noticed that on clear evenings, especially in fall or winter, that just before it goes completely dark, the sky has a deep, bottomless blue that merges with the dark. I think that is sunlight from over the horizon lighting up the late dusk sky.
I’ve seen this captured in a couple of paintings but the real purpose for the song, At Dusk, is to pay attention to things like that and enjoy them for what they are.
The song is available on all streaming services, and if you do not have a music service, you can access the song on YouTube: https://youtu.be/O99bsQSL1d8
If you would like to check out the lyrics: http://craigjhansen.com/at-dusk