I have worked on many cars.. From E30s to E46 M3s.. And everything in-between. I have seen no correlation between the color of the key and EWS. I think it depends on the car.
E46 M3 silver
E30 silver- some gold
E36 silver and gold.
The funny thing is that sections of my key are gold.. Where the silver is wearing off.. and mine does not have EWS.