support alpha in color dialog, see #14127

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73640 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/carbon/colordlgosx.mm

@@ -106,6 +106,7 @@ bool wxColourDialog::Create(wxWindow *parent, wxColourData *data)
     NSAutoreleasePool *thePool;
     thePool = [[NSAutoreleasePool alloc] init];
 
+    [[NSColorPanel sharedColorPanel] setShowsAlpha:YES];
     if(m_colourData.GetColour().IsOk())
         [[NSColorPanel sharedColorPanel] setColor:
             [NSColor colorWithCalibratedRed:(CGFloat) (m_colourData.GetColour().Red() / 255.0)