The Chart3DLabels object has a DefaultStyle that controls attributes of all labels (font, colors, border). Each of the labels also has its own individual Style inherited from this Default style. Setting attributes of the individual style overrides the attributes of the DefaultStyle.
For instance, in the following code the background color of the default style can be set to gray:
C1Chart3D1.ChartLabels.DefaultStyle.BackColor = Drawing.Color.Gray
•C#
C1Chart3D1.ChartLabels.DefaultStyle.BackColor = Drawing.Color.Gray;
All existing labels will have a gray background (if not deliberately set otherwise), and all new labels created will also adopt a gray background.