There are plenty of importers of the Mustang here in the UK and in other European countries. They all have to pass a single vehicle type approval test to bring them in line with European lighting regulations but as a single import, they oftendon't have to comply with every safety regulation as the FMVSS certification is taken to meet equivalent European specifications.
The lights on the GT500 were aftermarket units and are red stripe outer (light/brake) middle white (reversing light/orange indicator bulb) and inner red (high intensity fog light). Most people tend to put an orange bulb in the reversing light and hang an extra reverser underneath, along with a fog light because you then get to keep the "3 bars lit" appearance instead of a single bar.
As you can see here, mine has LEDs mounted on the stock lights and a fog light slung underneath: