Why are some blades black (dark gray) and some shiny?
When we were making all of our blades here in our small backyard shop, they were all gray/black because we didn't grind them flat after heat treating. The gray/black is a very thin coating of iron oxide that forms during heat treatment. Several years ago, we started having some of our blades made by others (don't worry, the alloy and hardness specifications are the same); large shops that cut the blades with lasers and wet-grind them to thickness after heat treating. The thicknessing makes them nice and flat and shiny-bright.
We still make many of our products right here in the backyard shop (still mostly by Larry, even after all these years) and they're the ones now that are gray/black with our debossed logo.