class ColorData
{
public:
    void setColor();
    SPColor getColor() const;

    void setAlpha( gfloat alpha );
    gfloat getAlpha() const;

    void setColorAlpha( const SPColor& color, gfloat alpha, bool emit = false );
    void getColorAlpha( SPColor &color, gfloat &alpha ) const;

    void setSubmode( guint submode );
    guint getSubmode() const;

    Gtk::Widget *getColorWheelSelector() {
       ColorWheelSelector* selector = new ColorWheelSelector(*this);
       _signal_update_internals.connect(sigc::mem_fun(selector, &ColorWheelSelector::on_update_internals));
       //I cannot make up a way to store sigc::connection in case of disconnecting ColorWheelSelector
       //sth like g_signal_handlers_disconnect_matched would be great
       return selector;
    }

    Gtk::Widget *getColorICCSelector();
    Gtk::Widget *getColorScales();
    Gtk::Widget *getColorNotebook();

private:
    sigc::signal _signal_update_internals;
};

ColorData::setColor( const SPColor& color ) {
   _color = color;
   _signal_update_internals.emit();
}



class ColorWheelSelector : public Gtk::Widget
{
    ColorWheelSelector(ColorData& data);

    void on_update_internals();

    // all other necessary Gtk::Widget methods
}



class ColorSelectorUser
{
private:
    ColorData _selected_color_data;

public:
    ColorSelectorUser() {
        Gtk::Widget *wheel = Gtk::manage(_selected_color_data.getColorWheelSelector());
        Gtk::Widget *scales = Gtk::manage(_selected_color_data.getColorScalesSelector());

        //add wheel to a container and forget
        //add scales to a container and forget
    }

    void some_method_involving_setting_color {
       _selected_color_data.setColor(color);
    }
}