Created attachment 147775 [details] grey is not black SUMMARY The selected accent colour is never actually used. Instead, a selection of similar but different colours are used. STEPS TO REPRODUCE 1. Open system settings -> Appearance -> Colours 2. At the top of the page, click Use Accent Colour -> Custom 3. Select full black in the palette widget. 4. Click "Apply" OBSERVED RESULT Selected items have a grey background. EXPECTED RESULT Selected items have a black background. SOFTWARE/OS VERSIONS Windows: macOS: Linux/KDE Plasma: (available in About System) KDE Plasma Version: KDE Frameworks Version: Qt Version: ADDITIONAL INFORMATION This happens regardless of the custom colour selected - the actual colour used will always be slightly lighter, unless you pick solid white. It also happens regardless of the Plasma and Application theme selected.
See also Bug 442820, which is a more specific variant of this issue as applied specifically to the dark version.
Yes, what is happening is that the accent colour is being blended with the normal background to create the selected background. This leads to light themes looking washed out and dark themes looking muddy. What should actually (imo) happen is that the accent colour should be used directly for selected item backgrounds, and the other colours should be created dynamically. Currently the accent colour seems to be used unmodified only for hyperlinks which (again, imo) should always be blue or purple.
*** Bug 442820 has been marked as a duplicate of this bug. ***
*** This bug has been marked as a duplicate of bug 442820 ***
*** This bug has been marked as a duplicate of bug 451698 ***