So the last time I was in a plane during a sunset I saw something new: a series of layered colors along the horizon, from red at the bottom through orange, yellow, green, then ending with the blue of the higher sky. This was not "the glory," a circular rainbow seen on clouds below a plane, but a series of flat lines parallel to the horizon encompassing at least 90 degrees or more (that is, 1/4 of the sky, at a considerable distance from the sun itself). The sun was also low and quite red; indeed, it was neither above nor below the colored stripes, as is the case for most ordinary rainbows (including "the glory"), rather it was on the same level as them, separated by some clouds. I understand that the color is due to scattering, and it makes sense that closer to the horizon I'm looking through more air than at higher angles so this shifts the light more to the red. What I'm wondering is if this phenomenon has a distinct name, and if it only appears under unusual conditions or is a common sight from planes at sunset or sunrise.
It is simply called the sky's colors at sunset, or twilight colors. These colors can be seen as well from the summit of a mountain, from International space station, and from the surface of the earth.
Sunset from Internation space station. Credit: Expedition 15 Crew, NASA (downloaded from wikimedia commons)
jkien's picture is in the right ballpark, but the bands I saw were more distinct than this, especially in the green & yellow, which here are almost completely muted and blurred. However his suggestion that this happens often at twilight inspired another google keyword search, and this time I found an even more specific suggestion: "airglow," as in the picture below. This is picture 11b from the page https://clarkvision.com/articles/color.of.the.night.sky/ discussing airglow, cf. also https://en.wikipedia.org/wiki/Airglow
While airglow is most visible after sunset, Clark attributes the strong green in his picture to airglow. In my case, the sun was above the horizon, but partly obscured by clouds. I didn't take a picture or record the time (and was crossing time zones anyway) so it is now impossible for me to say exactly how bright the sun was. So either this was a case of strong airglow with an obscured sun, or just a particularly sharp set of twilight color bands, or the latter with airglow contributing to the green band in particular. I will consider this question answered unless someone else wants to contribute further soon.
You may have seen a circumhorizontal arc. Seen here it is seen in clouds towards the bottom of the photograph; https://en.wikipedia.org/wiki/Rainbow#/media/File:A_Double_Rainbow_Halo_on_June_1,_2014,_at_1-57_PM.jpg