def MakeBitmap(self):
-        bdr = 10
+        bdr = 8
         width, height = self.GetSize()
+
+        # yes, this is weird, but it appears to work around a bug in wxMac
+        if "wxMac" in wx.PlatformInfo and width == height:
+            height -= 1
+            
         bmp = wx.EmptyBitmap(width-bdr, height-bdr)
         dc = wx.MemoryDC()
         dc.SelectObject(bmp)
         self.SetBitmapDisabled(bmp)
         self.SetBitmapFocus(bmp)
         self.SetBitmapSelected(bmp)
-
+        self.Refresh()
+        
 
     def OnChange(self):
         wx.PostEvent(self, ColourSelectEvent(self.GetId(), self.GetValue()))
         if changed:
             data = dlg.GetColourData()
             self.SetColour(data.GetColour())
-
         dlg.Destroy()
 
         # moved after dlg.Destroy, since who knows what the callback will do...