Wayland: how to get rid of blue color in title bar?

[mike155]

Whenever I start Qt- or KDE- based programs in Wayland mode ("QT_QPA_PLATFORM=wayland-egl"), the color of the title bar is blue.

What is the best (or easiest) way to change the color of the title bar to gray, so that it looks as if I the program was running in X11 mode?

My environment:

• Wayland compositor: Weston or Mutter / Gnome 3.22
  
• Qt: 5.7 or 5.9
  
• KDE apps: current unstable
  

Examples:

[asturm]

Why do you set QT_QPA_PLATFORM?

[mike155]