I've just done a DarkSky download from the AltAppStore and get this log:
2016-11-23 13:27:15.491 luup_log:4: AltAppStore : updating icons in icons/ ...
2016-11-23 13:27:15.491 luup_log:4: AltAppStore : updating device files in ./ ...
2016-11-23 13:27:15.557 luup_log:4: AltAppStore : ... 0 icon files
2016-11-23 13:27:15.557 luup_log:4: AltAppStore : ... 4 device files
2016-11-23 13:27:15.557 luup_log:4: AltAppStore : DarkSky Weather update completed
...which clearly shows that, indeed, no icons are downloaded.
The AltAppStore database has this entry under the DarkSky Repository field:
[{"type":"GitHub","pattern":"","source":"999LV/DarkSkyWeather","folders":[""," icons"],"versions":{"1":{"release":"0.2"},"2":{"release":"0.3"}}}]
which looks OK... but isn't.
Turns out that there is a leading space in the icons folders definition: " icons" should be "icons".
I've fixed that and re-installed from the store:
2016-11-23 13:45:00.264 luup_log:4: AltAppStore : updating icons in icons/ ...
2016-11-23 13:45:00.264 luup_log:4: AltAppStore : updating device files in ./ ...
2016-11-23 13:45:00.297 luup_log:4: AltAppStore : ... 11 icon files
2016-11-23 13:45:00.297 luup_log:4: AltAppStore : ... 5 device files
2016-11-23 13:45:00.297 luup_log:4: AltAppStore : DarkSky Weather update completed
... success!