We know -- it's a jumpsuit, so it doesn't really have a top. However, if you're trying to get this look at home, it might be easier (or more practical) for you to find a black halter with a deep V and pair it with a pair of black pants or dark jeans. Notice that it's not skin tight (and also that it's being held in place by probably half a roll of boob tape).
From Red Carpet to Your Closet: Cat Deeley at the American Idol finale