expression.Transparency
expression Required. An expression that returns one of the objects in the Applies To list.
Remarks
The value of this property affects the appearance of solid-colored fills and lines only; it has no effect on the appearance of patterned lines or of patterned, gradient, picture, or textured fills.
Example
This example sets the shadow of shape three in the active document to semitransparent red. If the shape doesn't already have a shadow, this example adds one to it.
With ActiveDocument.Shapes(3).Shadow
.Visible = True
.ForeColor.RGB = RGB(255, 0, 0)
.Transparency = 0.5
End With