wxGUI/nviz: SetMaskColour causes problems on macos with wx 4.1.0 (#787)

gui/wxpython/gui_core/widgets.py

@@ -499,7 +499,7 @@ class SymbolButton(BitmapTextButton):
         elif usage == 'pause':
             self.DrawPause(dc, size)
 
-        if sys.platform != "win32":
+        if sys.platform not in ("win32", "darwin"):
             buffer.SetMaskColour(maskColor)
         self.SetBitmapLabel(buffer)
         dc.SelectObject(wx.NullBitmap)