anchor.diff:    // Called by either an external control (aka gradient_colorstops_control)
     void externalColorChange(ColorData stop) {
       _transmit = false;
  +    externalStop = stop;
       
       // An external control is telling us to switch to a new color configuration.
       color = stop.color;
  
positive.code:       stop.color = color;
        stop.whiteness = bright;
        stop.darkness = dark;
        _colorChangeCallback(stop);
      }
    }
  
negative.code:   ColorValue colorBoxValue = new ColorValue();
    ColorValue colorValue = new ColorValue();
    
    ColorData externalStop;
    
    bool _down = false;
    BaseSlider target;
    
  