The opacity of the interior, from 0 (completely transparent) to 100 (opaque).
The default is 100.
Example
This example sets the Fill to 50% opacity.
Var a As New ArcShape
a.ArcAngle = 1.57
a.StartAngle = -1.57
a.BorderOpacity = 100
a.BorderColor = &c0000ff
a.BorderWidth = 2.75
a.FillOpacity = 50
a.FillColor = RGB(255, 0, 127)
g.DrawObject(a, 100, 100)