Few icons don't match the rest in panel

[bungadrum]

In the XFCE panel a couple of system tray icons don't match the rest can you update these to look monochromatic ?

VLC Media player (Flatpak)
Viber (Flatpak)
Liferea (Deb package)

[ZenithMonk]

It probably makes sense to update all tray icons (from other DEs too) to look monochromatic, especially with the recent symbolic icon change on KDE 6.