Stop using GDK functions for parsing colours names

This shouldn't be necessary now as they use the same CSS colour names
that we use too by default and like this switching to "Traditional"
colour names also changes wxGTK behaviour to use wxMSW colour values.

include/wx/gtk/colour.h

@@ -49,8 +49,6 @@ protected:
     virtual void
     InitRGBA(unsigned char r, unsigned char g, unsigned char b, unsigned char a) override;
 
-    virtual bool FromString(const wxString& str) override;
-
     wxDECLARE_DYNAMIC_CLASS(wxColour);
 };
 

interface/wx/gdicmn.h

@@ -974,7 +974,13 @@ public:
             wxTheColourDatabase->UseScheme(wxColourDatabase::Traditional);
         @endcode
 
-        during the application initialization.
+        during the application initialization. Please note that in the previous
+        versions wxGTK already used CSS colour values, unlike all the other
+        ports, so @c Traditional is not actually backwards compatible for
+        wxGTK, but does make the colour values consistent across all platforms
+        and the same as had been used by wxMSW and wxOSX before. In other
+        words, to obtain 100% compatibility with the previous versions, the
+        UseScheme() call above should be made for all ports except wxGTK.
 
         Note that the colour names defined only by wxWidgets, which notably
         includes all colour variants with spaces in their names, are still

src/gtk/colour.cpp

@@ -253,24 +253,3 @@ wxColour::operator const GdkRGBA*() const
     return c;
 }
 #endif
-
-bool wxColour::FromString(const wxString& str)
-{
-#ifdef __WXGTK3__
-    GdkRGBA gdkRGBA;
-    if (gdk_rgba_parse(&gdkRGBA, str.utf8_str()))
-    {
-        *this = wxColour(gdkRGBA);
-        return true;
-    }
-#else
-    GdkColor colGDK;
-    if ( gdk_color_parse( str.utf8_str(), &colGDK ) )
-    {
-        *this = wxColour(colGDK);
-        return true;
-    }
-#endif
-
-    return wxColourBase::FromString(str);
-}