[stable10] Use darker colors for app icons in app management

[MorrisJobke]

Backport of #834

I tested it with the news app (which has an old icon) and it works really nice :)

@Mar1u5 @juliushaertl @raghunayyar @Bugsbane @schiessle @rullzer @nextcloud/designers Please review :)

[mention-bot]

@MorrisJobke, thanks for your PR! By analyzing the annotation information on this pull request, we identified @DeepDiver1975, @jancborchardt and @PVince81 to be potential reviewers

[juliusknorr]

works 👍

@MorrisJobke btw. there are no new icons, we will stay with the white icon files and always use the inverting for now.

[MorrisJobke]

@MorrisJobke btw. there are no new icons, we will stay with the white icon files and always use the inverting for now.

Ah right ... I mixed this up with the theming: like nextcloud/notifications#9

Thanks :)

[schiessle]

looks good 👍

[jancborchardt]

@juliushaertl always remember to delete the branch when it has been merged. ;) (Just did it)

[juliusknorr]

@jancborchardt Ok, will do next time. Always thought that would be happening automatically. ;)

[jancborchardt]

@juliushaertl yeah, that would be nice right? :D Mailed Github about that some time ago and they said it’s on their roadmap but won’t happen in the near future unfortunately.