In order to add a background to the iframe element, I need to add the attribute allowtransparency="true" to the formatter. Unfortunately, I couldn't find a reference to the actual tag or the lightboxFrame class anywhere in the formatter or the .module.

http://www.adventperformance.com/store/cold-air-intakes shows you how it should function in firefox or safari (click on the text link, not the picture), but in internet explorer it rejects the background property and displays a white one instead.