Prefer
    ParamColor::ParamColor(const gchar *name, const gchar *guitext, const gchar *desc, const Parameter::_scope_t scope,
                           bool gui_hidden, const gchar *gui_tip, Inkscape::Extension::Extension *ext,
                           Inkscape::XML::Node *xml)
        : Parameter(name, guitext, desc, scope, gui_hidden, gui_tip, ext)
        , _value(0)
        , _changeSignal(0)
    {
over
    ParamColor::ParamColor(const gchar *name, const gchar *guitext, const gchar *desc, const Parameter::_scope_t scope,
                           bool gui_hidden, const gchar *gui_tip, Inkscape::Extension::Extension *ext,
                           Inkscape::XML::Node *xml)
        : Parameter(name, guitext, desc, scope, gui_hidden, gui_tip, ext), _value(0), _changeSignal(0)
    {