Black keys generally refer to those used with credit cards. There are not many black keys in certain treasures. Generally, the ones with very low prices are keys from the Russian area. If you often use the keys from the Russian area, you may get a small yellow letter or a small red letter. It depends on luck. It is recommended to use less certain treasure keys. They are basically from the Russian region. If you really want to buy them, just buy those games that are really unavailable in the region.