Icebox the FAA 1st class medical (including the signal light practical test) is in full compliance with ICAO You will not be limited to US airspace. N reg aircraft is the only limitation and there are more N reg aircraft than all the others put together. The JAA's position on this and many other medical issues is way behind current best practice. If all these colour deficient pilots (there are at least 8000 in the US) were unsafe how come they are operating safely all over the world including flying for US airlines into and out of Europe?
Recently in the light of Accident experience or more accuratley lack of accident experience (stretching back to 1934) the FAA dropped the requirement for a waiver or as it was officially called A SODA. Now if you fail all other tests and pass the signal light test you are issued with a letter of evidence stating that you meet the standards. this letter is good for life.
The main issue here is the actual testing. All the plate tests and the lantern tests like the holmes wright and the farnsworth do not actually measure what you are seeing they measure 'how' you are seeing it. The colours presented are not red or green but are carefully arranged to be confused by individuals who are even slightly colour deficient. Based on the ishihara test I am unable to tell the difference between red and green, How then was I able to tell the FAA inspector the correct sequence of colours at a distance of 1500ft? the answer is simple the signal light test actually presented me with red and green and white, the ishihara test uses different shades of complimentary colours and the lantern tests use carefully selected wavelenths that are for instance reddish green and greenish red also the holmes wright lantern when it presents white light presents a greenish white specially to identify Green deficient persons.
In the real world red is red green is green and white is white.