All steels can and do rust, tarnish, and discolor over time and with use. Stainless steel just takes longer to do that, but it will. Same thing for the D series steels. Adding chromium and nickel to steel just slows that rusting and discoloring down. The only way to keep them "mirror bright" is to clean and oil them after use, and often. And don't store them in leather - the tanning chemicals react with the steel.
Stainless steel is also a lot harder to forge and work than the carbon steels, and a lot harder to re-sharpen once it gets dull. In the opinion of most professional knife makers, stainless makes for a lesser quality knife blade than the carbon steels. They make knifes using stainless simply because the market demands it.
There is no "best steel" for knife making. Each steel alloy has it's good points and bad points. Some are easier to sharpen, some hold an edge longer. Some are more shock resistant, some bend more than break/chip. Each use of a knife has a type of steel that would be better for it. But most general purpose knives tend to be forged from steels like 1095 or O1.
Having to clean/oil a carbon steel knife more often than a stainless steel knife is a small price to pay for a better overall using knife.
I have made several knives from 1095 carbon steel, and I several knives I always use made from 1095 and O1. I have a couple stainless steel knives I picked up over the years. They stay buried somewhere in the junk drawer. I'll take a carbon steel knife anytime. And I'm not worried about discoloration. Mirror finishes are for a display case - not a working knife.
Just my humble thoughts to share. Take them as such.
Mike Ameling