So I pulled out some ammo that I had stored in ammo cans with decicant. some rounds appreared to have dark spots starting to form and the bullet itself seemed to be darker and no longer bright. Only been in there for a year or so. Stored in the can in the cardboard boxes, is that my problem?

The cardboard is the issue, moisture, glue, etc.

My .02

thats what I'm thinking as well. Will hard plastic do anything to the life of ammo? I guess Im gunna have to remove all the cardboard and figure out a way to tell eaches apart.

Where were they stored?  In the house (room temp) or in the garage / basement.

Likely this.

I've stored loose ammo in cans for years while periodically changing desiccant packages.  Cardboard does have the ability to store a fair amount of moisture before being sealed in an ammo case.

Your ammo is still good to go, and don't let cosmetics get you down unless there's evidence of corrosion which you haven't indicated.  Also possible is the rubber seals of your ammo cans is degraded, depending upon how old the ammo can is.  If this is the situation, and you live in high humidity (likely not in NY), you may find an added measure of security by finding a local dive shop and purchasing some silicone grease for O-rings.  Lightly apply to the rubber seal and that should add some added measure of security moisture security to your ammo can.

I don't believe hard plastic will offer any benefits.  After living in Florida for a year, noticeable lead corrosion on my reloads was apparent.  Since you don't live in that humidity/salt environment, I would stick with your ammo cans, as they offer a tighter seal against the elements––that's why our armed forces uses them.

I ment the hard plastic having any negitive effects. aka 20rd sleave they came in.

Ammo cans should be gtg, pretty new. Im dumping everything out of the boxes and throwin in new decicant.

As for now it looks cosmetic, but I don't want it to eventually ruin the ammo as this is my HD/SHTF ammo.

How much dessicant are you putting in and how often are you opening the ammo cans?  

If you are opening them every night or every week to lust at the stash you have due to the current short supply, you need to replace the dessicant packs.  

If you only open them once a year, then I agree with everything said in this thread.

It depends on the cardboard, some but not all can cause tarnishing. Notice some ammo such as 6.5 Swede, DAG 308, can corrode against the cardboard boxes even inside of battle packs. That's because many types of paper have an acidic pH, this is why photographers have to buy special "acid-free" cardboard boxes, albums, etc.. when archiving print and film. To be safe, I try to avoid paper when storing ammo.

I dump rounds out of the boxes they come in, put them in freezer quart ziplock bags, 100 rounds/bag, then throw a desiccant pack in.