code: public void setNavigationBarTintEnabled(boolean enabled) {
          mNavBarTintEnabled = enabled;
          if (mNavBarAvailable) {
              mNavBarTintView.setVisibility(enabled ? View.VISIBLE : View.GONE);
          }
      }
docs: Enable tinting of the system navigation bar.
  
  If the platform does not have soft navigation keys, is running Jelly Bean
  or earlier, or translucent system UI modes have not been enabled in either
  the theme or via window flags, then this method does nothing.
  
  @param enabled True to enable tinting, false to disable it (default).