When opening Signal Desktop Beta with --start-in-tray it only shows a white rectangle as the tray icon

The white rectangle is Signal
Expected result: Icon should be signal icon
Kubuntu 17.10
Signal Desktop v1.1.0-beta.4
I did not try on Kubuntu, but on Arch I noticed that having libappindicator installed breaks the icons of electron apps in the KDE Plasma tray, with the same behaviour you described.
With the new notification count feature the tray icon shows about a quarter red circle segment in its lower right (-> screenshot).

So possibly the white tray icon problem is in fact an icon scaling problem and the white area, that is my tray icon so far, is in fact a white part of the speech bubble in the signal icon?
Yes, it seems so. Apart from the scaling issue, does the tray icon work? Can you minimise/restore the window from the tray and open the context menu (right click on the tray)?
Sorry if I forgot to specify, but the behaviour I observed in my previous comment (with libappindicator installed on Arch/KDE) was also a scaling problem of the image (at the time I noticed that by repackaging Signal using tray icons of different sizes). In that scenario, I also noticed that the interaction with the tray icon was broken. Is libappindicator installed on your system?
Yes, hiding/unhiding the window using the tray icon works (and always worked).
Yes, the packages libappindicator1 and libappindicator3-1 are installed.
Interestingly removing libappindicator1 would also remove signal-desktop-beta.
Same problem with KDE4 on Ubuntu 14.04.
same issue on kubuntu 16.04.
Same issued around here, Manjaro KDE (Arch/KDE) with lib32-libindicator-gtk2/libindicator-gtk2 installed since they are used by steam-native.
White square logo with half red with notification.
Launch Signal with XDG_CURRENT_DESKTOP=Unity signal-desktop --start-in-tray to temporary fix the problem.
Cheers, thanks for the workaround. Working fine here.
i can confirm that the workaround works.
I had the problem, that XDG_CURRENT_DESKTOP=Unity signal-desktop --use-tray-icon did not work with KDE's shortcuts, but env XDG_CURRENT_DESKTOP=Unity signal-desktop --use-tray-icon works with a fully working and shown tray icon.
@mpsdskd When you say "fully working and shown tray icon" do you mean one that shows a Signal icon or the square white one?
@cdysthe Have you tried the workaround suggested by https://github.com/signalapp/Signal-Desktop/issues/1876#issuecomment-363653689? This is working for me using the latest KDE (see screenshot with submenu expanded).

@kroka Had some problems getting it right but have a shortcut now with XDG_CURRENT_DESKTOP=Unity; "/opt/Signal Beta/signal-desktop-beta" --start-in-tray which works with icon. I was so surprised it didn't work out of the box since all other messaging applications I've used has this working. Still can't toggle the window by clicking the icon. Would be good to have that also.
Gentoo KDE user here. The XDG_CURRENT_DESKTOP env change did not work for me. Only uninstalling libappindicator worked. I just unset the trayicon use flag for games-util/steam-client-meta since it was the only thing I had depending on it.
Icon is properly showing on Fedora 31 KDE when starting with --use-tray-icon --start-in-tray.
Most helpful comment
Launch Signal with
XDG_CURRENT_DESKTOP=Unity signal-desktop --start-in-trayto temporary fix the problem.