Panel color is set to black but text color is not white.
Right click top panel, "Panel", "Panel Preferences...", "Appearance" tab, set "Style:" to Solid Color, click "Color:" box. Enter #000000 for "Color name:". Then click OK. The panel color changes to black, but the text color does not automatically change to white. Maybe there should be a "Text" label, with "Type:" and "Color:".