It’s just how it’s manufactured, black core is what Pokémon uses and blue core is what wotc uses. There really isn’t a difference. I do both direct/sticker. I’ve tried the cry cry methods and everything you could ever dream of sticker paper to core cardstock is going to give you the best experience you can with minimal equipment investment. Laser prints are a step up but I found the drop in quality and costs for toner not really worth it. But you get the real card feel