When it comes to BB Weapons so far you don´t have to be worried about reproductions (yet) since like Bachamn mentioned above for these it doesn´t really pay of for those who produce them since although some can be harder to find they cannot be compared with the rareness/prices of the LB guns.
Concerning the issue discussed here there´s not a lot to say about it without having a little bit more background info since the condition of the picture ain´t really strong to see a solid difference and/or to verify that its a weapon that might belong to the Greek BB (GBB) or the Spanish Bestias de Combate.
At this moment I´d say its not related to either GBB or BDC since the Greek weapons are normally much lighter than the original BB weapons while the BDC are a bit darker but they´re showing a deeper gold color.
That said I´ve had quite some weapons in hand over time and I can remember having seen a similar difference with the Buffalo weapon but also among other brown Serie 1 weapons probably due to aging and or the fact its somehow been effected by an external influence. So for now my guess is that it would be a normal BB weapon which somehow has changed a little in color.
But with more background info about the origin of your bag of weapons and a better pic we might be able to tell a little more.
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