This example sets the depth, extrusion color, extrusion direction, and lighting direction for the 3-D effects applied to shape one on myDocument
.
Set myDocument = ActivePresentation.Slides(1)
With myDocument.Shapes(1).ThreeD
.Visible = True
.Depth = 50
'RGB value for purple
.ExtrusionColor.RGB = RGB(255, 100, 255)
.SetExtrusionDirection msoExtrusionTop
.PresetLightingDirection = msoLightingLeft
End With