The yellow and blacks are the same blade, and they are both platinum coated. In fact, they only currently manufacture 1 grade of blade regardless of the exterior packaging. This has been probably answered before, I apologize. I went as far as emailing the Feather Co. and got a response confirming this.
However, there is one guy selling the black stock from Singapore, it is possible that this is old stock because the underside of the cardboard inserts were beginning to tarnish. Just blades perform just the same though. I have learnt that the current stock has a bar code sticker on the outside plastic wrap of each pack, and a lot number stamped on each individual pack. Ntguys on eBay has the freshest stock to my knowledge.
However, there is one guy selling the black stock from Singapore, it is possible that this is old stock because the underside of the cardboard inserts were beginning to tarnish. Just blades perform just the same though. I have learnt that the current stock has a bar code sticker on the outside plastic wrap of each pack, and a lot number stamped on each individual pack. Ntguys on eBay has the freshest stock to my knowledge.