Using "Settings -> Color Theme" I changed theme to "Dark Breeze". After that I wanted to change also color scheme for editor. Unfortunately I wasn't able to do it. In "KDevelop Settings -> Editor -> Fonts and colors" I selected schema "Breeze Dark". After that "Apply" button didn't change its activity, so still was not active. Pressing "OK" didn't bring effect, so still is "Normal".
Please ignore this. All is fine.