It's good that you're checking the date code, so many people don't do this. An international study has shown that 'new' tires with date codes of 6+ years are too old and dangerous for use. Numerous cases have been found where 'new' tires that were actually 6+ years old when bought had numerous failures with the treads catastrophically coming off. In that same study they had professional drivers in SUV's who were prepared for a blowout travel at highway speeds on a test track. When the tire did blow, the drivers were unable to maintain control despite being prepared for it to happen.
This type of thing has lead to deaths from tire blowouts on the highway. One such case was a father who had just put 'new' tires on his son's suv. His son and a friend were heading off to college. A few hundred miles later, one of the front tires blew out on the highway causing a fatal accident killing both.
In all the studies it was impossible to detect any flaws in the tires from visual examination. What was determined was that the rubber was too brittle and ended up breaking down while under pressure. In the EU they made it mandatory for all tires exceeding 6 yrs on the shelf to be recycled or destroyed. In the US the tire industry continues to refute the findings and denies there is any problem to worry about.
As for you tire, with it being 3 years old it should still be ok. What does sort of concern me is you saying it's discolored. I would say to wash them off with just water and a good scrub brush. After they dry if they still look discolored I would send them back. Better safe then sorry.
