Color variants

[Madis0]

E.g. white, black, blue, similar to ChromeOS Plasma.

[Zren]

It's controlled by your color theme. Edit a color theme and change the "titlebar" colors.

Or edit ~/.config/kdeglobals directly:

[WM]
activeBackground=60,59,55
activeBlend=60,59,55
activeFont=Noto Sans,10,-1,5,50,0,0,0,0,0
activeForeground=255,255,255
frame=0,0,0
inactiveBackground=60,59,55
inactiveBlend=60,59,55
inactiveForeground=200,200,200
inactiveFrame=0,0,0

[Madis0]

For now I did indeed use a color scheme for it, but since the base is gray it always needs a higher saturation color to get the intended result.