This is the Spectrum Classic Colors theme locked with the Strawberry Quartz color scheme so it stays rose regardless of the color scheme you are using. Use this if you want your panel and widgets to be rose, but to have different colored windows. Contrast issues may be present and folder colors for the desktop are lighter than the color scheme.
This plasma theme is used in Spectrum Strawberry Quartz. For variants, check out the Colors Collection and for pure dark and light themes check out the Eclipse Collection.
Opacity can now be changed using the script included with theme. Navigate to the theme's directory and pass a value from 0 to 99 to the script.
$ cd .local/share/plasma/desktoptheme/spectrum-classic-strawberryquartz
$ ./changeOpacity 43
Have you tried turning it off and on again? Sometimes plasma assets will not update and some may still be themed according to something you previously had set. This can usually be fixed by restarting.
To restart just plasmashell, open KRunner with "Alt + F2" to execute the following: