What if your whites have a grayish (or blueish, pinkish, greenish, yellowish) hue to them? Try this:
Go to Enhance, then Adjust Color, then Remove Color Cast.
Click on a part of the photo that is supposed to be white (or you can also click on anything black or gray). The grayish (or blueish/pinkish/greenish) hue will disappear. If it doesn't, or it still isn't to your liking, keep clicking different white/ivory parts of your picture until you get an adjustment you're happy with.
Attached are three variations of the same picture: the original (kind of greenish), and then two adjusted versions. Just play around and pick what you like best. The variations in this particular photo are pretty subtle, but sometimes, the variations can be dramatic. For example, my early morning photos and cloudy day photos are very "blue." I tried to get a photo that would illustrate this better, but my picture perfect weather today just wasn't cooperating