Created attachment 166539 [details]
Image showing the system tray icon in black on a dark panel

SUMMARY
On a dark panel, the KMail system tray icon remains black and is near impossible to see in some odd situations, such as when the Breeze Twilight theme in Plasma 6.0.1 is selected.

AFAICT from quick testing, the KMail Color Scheme setting has no relation to the colour of the system tray icon.

STEPS TO REPRODUCE
1. Select Breeze Twilight under Colors & Themes -> Global Theme.

OBSERVED RESULT
A system tray icon that's very hard to see (see the kmail_system_tray.png image attachment).

EXPECTED RESULT
A white icon, matching other other Plasma icons.

Strangely, if I apply Breeze Twilight, and then Breeze Dark, the icon remains black and unreadable. However, if I apply Breeze, and then switch to Breeze Dark, the icon is now as expected in white.

If I then select Breeze Twilight for everything except "Colors", that gets most of the theme applied except it's still a dark theme which I do not want. However, at this point I can select Breeze Twilight again with all Appearance settings selected, and that will apply the correct colours everywhere but also for some reason leave the system tray icon white — so that's the bizarre work-around.

Or so I thought! As I was writing this, the system tray icon turned black again. It appears to revert as soon as the icon is updated, presumably by getting a new message, or more simply, by closing and re-opening KMail again.


SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.0.1
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2
Kernel Version: 6.7.8-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 32 × AMD Ryzen 9 7950X3D 16-Core Processor
Memory: 62.0 GiB of RAM
Graphics Processor: AMD Radeon RX 7900 XTX
Manufacturer: Micro-Star International Co., Ltd.
Product Name: MS-7D70
System Version: 1.0