The insert numbers are a real silver and not faded to a light gold color as most early inserts become. Compare the all blue 1675 GMT insert numbers to the all copper GMT insert.
The early all gold inserts had fat number fonts..Compare the number "8" for example on the all gold faded 1675 with the copper insert.
Now as far as the silver color, the early fonts in the picture are more of a light gold cream from fade. But copper is a real no fade silver and is an entirely a different insert when one looks closer. The serifs are different as well on the two inserts, as one can see for example in the number "4".
The all copper insert has the number fonts in silver not gold..BIG differance..same as the all blue bezel. These 1675 GMT inserts I believe were used in the late 1960's and 1970's on the two tone model 1675 gold bezel and SS cases. But maybe also found on just an all SS 1675 GMT.
The all blue GMT insert from my research was issued on military 1675's at first..
But with surplus the leftover all blue bezels were given to Rolex service centers and made available as an option to service customers in the 1970's till the stock ran out. I was also told by Rolex NYC that the service center watchmaker years ago when I submitted my 1675 for service, that an in-house parts book had the all blue Tudor Sub and Rolex GMT bezel pictured. One interesting note, was that Tudor had an all blue bezel on the 1970 Tudor Sub and Monte Carlo chrono model.