I have now modified the script so that instead of replacing white with transparency it floodfills all white parts with transparency beginning from all four corners. That way white parts of icons (e.g. Quicktime, Windows Media) will stay white and the icons look great on light grey backgrounds.

This sounds ideal! Glad you could make this work.

Because of that I would recommend adding a white background with CSS in these cases (mostly the black popup)

👍

I have now added a new release on https://github.com/Findus23/device-icons. Should I create a new pull request or wait until we have found a solution for Findus23/device-icons? (e.g. use as a composer package similar to piwik/searchengine-and-social-list)

@Findus23 shall we create new issue regarding finding a solution to package icons in Piwik core via composer or submodule etc. ?

If we can find a solution quickly then maybe it's worth waiting to push the new icons to KISS

@Findus23 shall we create new issue regarding finding a solution to package icons in Piwik core via composer or submodule etc. ?

see #11370

This should have greatly improved with matomo-org/matomo-icons@1161949