If it is platinum, it is plated and done post mint. The layer is very thin and of no real value. You can buy the plating solution at several jewelry supply stores on the net. The US mint never made any platinum cents. Jim
My wife has recently found a 1964D penny of a silvery color. Weight 2.65g, maybe a hair less; this is at the low end of the range of weights I got from a half dozen 1943 steel pennies, but nowhere near the 3+ g I got from pre-1982 (copper) pennies or the much lower (I doubt recall the exact number) weight of post-1982 (copper-clad zinc) pennies. The coin is slightly magnetic, but not as magnetic as a 1943 steel: it takes a stronger magnet to pick up this penny than the 1943.