The majority of the blades I use on the pocket knives and kitchen knives are made from either C70 of O1 carbon steel. Carbon blades are preferred because they can get a sharper edge and hold that edge better than knives made from stainless steel.
Carbon steel takes a little more looking after than stainless steel, but the patina that builds up over time gives your knife a little character and as it is a tool it will tell a story of its use.
Discolourations on your knife are normal, mainly because it is not a stainless steel, but don't panic! Oil the blade and scrub with a very light abrasive or a scratch free scourer to remove any spots and your blade will be undamaged. Kitchen knives look great with a bit of patina, which is why I add a forced patina to start with. The food acids you cut into will add to this look. Once you’ve used the kitchen knife it is best to wash and dry it straight away. Leaving it on the draining board will cause rust spots. These can be brushed off using the method above though.
With regards to pocket knife blades, wipe with an oily rag after use to help keep the blade in its best condition. If you keep it in a leather pouch then make sure your blade is oiled as the moisture from the leather will cause the steel to mark.
And one last thing... always oil the joint. To keep your pocket knife in the best possible condition add a few drops of oil where the blade makes contact with the spring. This will the blade open and close with a snap.