Looks like the letters are transparent. You can verify that by moving the Properties box on top of some other window that is not solid color.
The system that draws the text (called "GDI") dates back to Windows 95 and doesn't support transparency. So the darker the text is, the more transparent it gets (notice how the white text at the bottom looks fine). Software that supports glass needs to take special care when drawing text. Unfortunately the Properties page is not expecting transparency, so glitches like this are to be expected.