Bug 507622

Created attachment 183617 [details]
system settings and dolphin side by side as described.

SUMMARY
In system settings (info center too, but this report isn't about it) the sidebar is unable to properly display transparent or partially transparent colors. It instead displays them completely opaque with the reduced opacity seeming to be used as a modifier for the brightness instead.

STEPS TO REPRODUCE
1. apply transparent theme (alpha works fine, I'll add the ones I use if it will let me)
2. open system settings and another app side by side (I recommend dolphin, it typically works what I would call correct)
3. Compare the application of transparency

OBSERVED RESULT
the other app displays the transparency as configured in the color scheme while system settings instead displays a lighter version of the configured color in the sidebar, while the rest of it works as configured.

EXPECTED RESULT
The transparency is displayed as configured (i.e., transparently) across the entire app.

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 42
KDE Plasma Version: 6.4.3
KDE Frameworks Version: 6.16.0
Qt Version: 6.9.1
Kernel Version: 6.15.7-200.fc42.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 4600H with Radeon Graphics
Memory: 16 GiB of RAM (15.0 GiB usable)
Graphics Processor 1: AMD Radeon Graphics
Graphics Processor 2: NVIDIA GeForce GTX 1650
Manufacturer: LENOVO
Product Name: 82B5
System Version: Lenovo Legion 5 15ARH05

ADDITIONAL INFORMATION
I am using https://github.com/taj-ny/kwin-effects-forceblur instead of the normal KDE blur because the transparency I want would not be properly blurred with the normal effect. this is not the cause of the issue becuase with the normal blur on instead they are simply transparent without blur.