2.1.1673 Part 4 Section 188.8.131.52, spPr (Shape Properties)
For additional notes that apply to this portion of the standard, please see the notes for spPr, §184.108.40.206(a-c) .
a. The standard states that the grpFill element is a valid child of the spPr element.
Office will display an empty (invisible) shape fill for any diagram shape with a group fill, regardless of the fill of the parent group.