Majority of FRS running "tinted" headlights are actually running the non xenon ST170 headlights that are tinted as standard - nice easy swap over as well

Other option is to split the standard lights apart & paint the inside although a few people have snapped clips trying to heat them up & part them

Have a look on the RS Owners Club forum in the Mk1 Focus RS section if you get a chance as there are a few threads in there with pics relating to headlights