SUMMARY It's great that Plasma themes can follow the system color scheme now. How about an option to select a different color scheme for Plasma themes (separately from the system)? Including separate accent color settings: from current color scheme, from wallpaper, custom. In SystemSettings? Or in themes' settings? This way the default Breeze theme could replace both Breeze Dark and Breeze Light. And it would still follow the color scheme (and accent color), which the other two do not support.
What's the use case for this, out of curiosity?
Currently Kubuntu ships with a dark theme for Plasma and a light system theme. You cannot achieve this effect by using the Breeze Plasma theme, because with it the entire desktop can be either light or dark. And Plasma 's Breeze theme is the only one that follows system color (including accent color from the wallpaper). Using Breeze Dark theme for Plasma leaves you without the ability to have accent color from the wallpaper in Plasma widgets. The default blue color is always used in Plasma, which looks kinda off when the system theme follows wallpaper for accent color. Replacing Breeze Dark and Breeze Light themes with just a setting for the default Breeze theme seems reasonable.
Let's fix the issue of Breeze Dark not respecting the accent color, and then we'll see if there's still demand for allowing Plasma themes to select whole color schemes themselves. *** This bug has been marked as a duplicate of bug 444043 ***