When you are shooting with a bright white background it will often reflect in the top of the subject. In this case it takes away the color. The trick is to simply put something else outside the photo area for it to reflect. In the series of photos below the first one is a straight shot with one light lighting the piece and one shining on the background. This gives an even lighting although it's kind of flat looking but for our purposes it will work. You see how there is glare on the top and on the right side. In the second photo I put a black cloth over the background just barely out of the picture area. That made the top darker. For the photo on the right I simply took a black card and put it back to the side so the side picked up the reflection of the card and gave me some color there.

If black is too much, then use gray or simply take a card and cast a shadow on the back ground out of the picture area. To figure out where the problem is coming from think of the reflection like a pool shot. The camera is the pool cue and the top is the rail. Where the ball would hit the background is where the black card needs to be.