It's been my experience that D2 will in fact take some slight discoloration from some substances, more noticeable if highly polished. I think it's classified as a tool steel and not a true stainless steel. YMMV
So... I have a good hunting buddy who has a Knives of Alaska kit with the large hunting knife in D2 and the caping knife in 440C. He is not a knife aficionado by any measure. He dressed and quartered a whitetail using the kit and put it up dirty. The next season he pulled it out and proclaimed “ the large knife is ruin’t”, it took a thick dark patina with a few spots that were mild surface rust. So D2 will patina. It just takes more effort.
I've given up on getting mine to patina, anoyingly so... It might as well be stainless, since it wont patina to protect itself it, thus it will unfortunately rust. (I've rarely had a carbon blade rust, stainless does it easily..)
Yes, it was forced with vinegar. I'm pretty sure that was originally mine that he won in a giveaway quite a few years back. I had mixed results with forcing a patina on D2. A couple turned out good, but at least one came out really splotchy.
I think through regular use it would take quite a while for a natural patina to develop unless you constantly used it to cut acidic stuff.
D2 is a semi stainless. I think. Maybe 11% or 12% chromium. And like 2% carbon. So if it does rust its practically from neglect. You could force a patina. Bring white vinegar to a boil. Open your knife blade and use rubbing alcohol to remove any oils from the blade. Then put it tip down in a glass. Pour the hot vinegar in the glass slowly until its covering the blade and stops just short of the tang. Leave it in until it darkens up. If you see little bubbles you know its working. Remove and lightly buff with steel wool. Repeat until it reaches the shade you like.