This example adds a shape to slide one in the active presentation, sets the default fill color to red for shapes in the presentation, and then adds another shape. This second shape will automatically have the new default fill color applied to it.
With Application.ActivePresentation
Set sld1Shapes = .Slides(1).Shapes
sld1Shapes.AddShape msoShape16pointStar, 20, 20, 100, 100
.DefaultShape.Fill.ForeColor.RGB = RGB(255, 0, 0)
sld1Shapes.AddShape msoShape16pointStar, 150, 20, 100, 100
End With