Unofficial documentation for the iCloud Apple device image URL format

gistfile1.txt

https://statici.icloud.com/fmipmobile/deviceImages-9.0/iPhone/iPhone9,4-2-3-0/online-infobox__3x.png
                                                   A   B      C         D E F G

A: deviceImages version seems to determine the format of the image specifier (C, D, E, F)
B: device marketing name
C: device model identifier
D: color cover glass (front color)
   1 - Black
   2 - White
E: device enclosure color (back color)
   1 - Space Gray
   2 - White
   3 - Gold
   4 - Rose Gold
   5 - Stainless steel white (Watch only)
   6 - Stainless steel black (Watch) / Product Red (iPhone)
   7 - Gold 2 (?) / Edition (Watch only) / White Ceramic (Watch only)
F: unknown
G: image variant
   online-sourcelist.png
   online-sourcelist__2x.png
   online-sourcelist__3x.png
   online-infobox.png
   online-infobox__2x.png
   online-infobox__3x.png
   
Examples:

White iPhone X
https://statici.icloud.com/fmipmobile/deviceImages-9.0/iPhone/iPhone10,6-1-2-0/online-infobox__3x.png

Black iPhone 8 Plus
https://statici.icloud.com/fmipmobile/deviceImages-9.0/iPhone/iPhone10,2-1-1-0/online-infobox__3x.png

Gold iPhone 8 Plus
https://statici.icloud.com/fmipmobile/deviceImages-9.0/iPhone/iPhone10,2-2-3-0/online-infobox__3x.png

Black HomePod
https://statici.icloud.com/fmipmobile/deviceImages-9.0/HomePod/AudioAccessory1,1-1-1-0/online-sourcelist__3x.png

White HomePod
https://statici.icloud.com/fmipmobile/deviceImages-9.0/HomePod/AudioAccessory1,1-2-2-0/online-sourcelist__3x.png