Your white laundry items can often start to have a grey look to them due to a few things. You may live in a hard water area and deposits become fixed to the fibers, or it could just be a build up of detergent within the item. A vinegar rinse is all you need to get your whites white again.
Soak the item in a gallon of warm water water and 8fl oz of white vinegar. Then rinse in a cold water rinse. To keep your white in tip top condition, add about one third of a cup of white vinegar to your rinse cycle, you'll find that your clothes come out brighter and softer. Any vinegar smells should vanish after your clothes have dried.