This syntax works for me, you would need to determine the colors you wanted...

    With ActiveSheet.Shapes("Oval 1")
        .Fill.Transparency = 0.5
        .Fill.Visible = msoTrue
        .Fill.ForeColor.SchemeColor = 24
        .Fill.BackColor.SchemeColor = 34
        .Fill.TwoColorGradient msoGradientHorizontal, 1
    End With