fhoodAmon-Rukh is exactly right and he provided an informative link. The reason certain groups of Japanese steels are referred to by color is because that’s the color of the paper they are delivered wrapped in. Even though the link says Blue paper steels are more corrosion resistant than White paper steels, Blue steels are not anywhere near stainless and you can almost watch them rust if not properly cared for. I’m curious what hrc these knives were hardened to as well as exactly which Blue steel they are.
www.japaneseknifeimports.com/blogs/news/64514117-a-quick-summary-of-hitachi-carbon-steels-common-in-knives