Brass is a copper-zinc/nickel alloy so my understanding is that the brass at the various manufacturing plants may have had different copper contents whereby some had a more copper color than brass.
With some Gillette gold plated razors, If you see a copper cap, it could be the gold plating has worn or been polished off. I am no expert but have been researching vintage Gillettes some so please anyone, correct me if I am wrong.
I have Gillettes where the top cap is mostly gold with a little copper showing,
or half gold with the rest copper showing,
or all copper except for the gold concealed parts.
From left to right:
New Long Comb
New Short Comb
Pre War Tech
another Goodwill 160