I have shared how to keep whites white before. But I recently discovered a new way and I am very intrigued!
Mix one part Dawn dish washing liquid (the plain old blue kind, in the
big bottle that usually sits on your sink), with two parts hydrogen
peroxide (available at any drug store), pour it directly on the stain,
and watch it disappear like MAGIC. If it's a big stain, as was the case
with my dress, you can mix the same equation and add it to a bucket of
hot water and just dunk the entire garment in there. When I first set up
the little stain removal lab in my kitchen, I was hesitant but figured
things couldn't get any worse, so I just crossed my fingers, closed my
eyes, and dropped the whole thing in there. When it emerged sparkling
clean, I tore through my closet like a madwoman in search of stained
items I hadn't had the heart to throw away. And it worked on every
single one of them: chocolate, red wine, barbecue sauce, etc.