Hi, 

The sell-by dates on packaged cuts of meat are not hard and fast guidelines for when they are unsafe. Rather, these dates are the packagers best guest at how long the cut will keep good quality. The brown color you see is caused by a chemical reaction caused oxidation, and that's a sign that the raw meat is getting older and may not be best quality. That's to be expected if it's four days past it's sell-by date, but it's not necessarily unsafe.

Before you decide whether to throw it out, check the roast for any off odors and slimy or tacky texture. If you see any of those indicators, it's time to throw the roast out. If the meat does not have an off odor or slimy texture, you can still use it. Make sure to cook the roast to a minimum internal temperature of 145°F for safety.

Thanks for using Ask Extension,

Jared

Thank you!