There is a particular shade of pale brown hair, as opposed to blonde, that makes the gold of a tiara sort of disappear and Stephanie seems to it. Later, when the sun has had a chance to streak it naturally as it was for her wedding, the tiara would have looked more prominent.
The only thing that gives really delicate tiara's like this one a boost is to place them on top of a killer updo. This is not one as her hair lacks height and wisps of hair are all over the place, partially obscuring the tiara which they would not be had her hair had been dressed by a hairdresser using the same finishing products as those on Victoria and Sophia.