Screenshot from System Preferences>General.
In macOS Mojave 10.14.6 (current OS for me), and other versions close in age, the highlight color used throughout the system can be changed to any RGB color of your choosing, with "Other."
As you can see, the accent color lacks such a setting; the grey on the right is "Graphite" color. Can this accent color be changed in any similar way? The color choices provided are too limited for me.