Currently we use 0xefefefff as a background color for non ARGB tray icons,
which looks out of place (i.e does not fit the panel's background gradient).
Change it to 0x0b0b0bff to fix that.
https://bugzilla.gnome.org/show_bug.cgi?id=597148
// Used for the tray icon container with gtk pre-2.16, which doesn't
// fully support tray icon transparency
const TRAY_BACKGROUND_COLOR = new Clutter.Color();
-TRAY_BACKGROUND_COLOR.from_pixel(0xefefefff);
+TRAY_BACKGROUND_COLOR.from_pixel(0x0b0b0bff);
const TRAY_BORDER_COLOR = new Clutter.Color();
TRAY_BORDER_COLOR.from_pixel(0x00000033);
const TRAY_CORNER_RADIUS = 5;