http://www.artsmia.org/ no direct linking, but type in buchner in the search box, click go (hitting enter will not work) and you'll find her protrait and that or Moritz

Lucas Cranach Portrait of Anna Buchner, née Lindacker 1518
The website allows you to zoom in on different parts of the image. The fabric that looks darker than the main body of the gown is some sort of tissue (metallic cloth with twisted threads). Perhaps gold with orange silk.
When you zoom in on the open part just above the lacing, the bodice folds back, showing that in this case it is not a thick layer.