Either plated or an outdoor find that toned the color. In circulation the higher devices would wear off to the normal color. But if the coin is 5 grams, then it is not a cent plancet. It would have to be a zinc planchet with that date and weigh 2.5 grams. (exactly half the weight of a nickel. The devices on a nickel struck onto a cent planchet would not be centered with the rims showing. It would look like this:
Reminds me of a post-1947 two-shilling piece I found on the beach as a teenager. It was dark brown. 10p was a lot of money to me in those days. I remember rubbing it in the sand on the beach, trying to clean it in the sink and then polishing it with the cloth my Mom used for her silver. (I wouldn't treat a collectible coin that way, but I just wanted to spend it). I could never quite get rid of the copper color, and it looked rather like Beachbabi's nickel when I'd finished it, but at least the bus driver accepted it, although he did comment that it was a funny color!