Can't change the format of a Shapes collection

[Torquemada]

I have 20 shapes on Sheet2 and I want to format them all identically without looping. I put the following in a Workbook:

Public sr As ShapeRange
Private Sub Workbook_Open()
Sheets("Sheet2").Shapes.SelectAll
Set sr = Selection.ShapeRange
sr.Fill.ForeColor.SchemeColor = 12
End Sub

This works fine. Now I go to Sheet2 and try to change all the shape colors to something else with this code in a module:

Public sr As ShapeRange
Sub ChangeColors()
sr.Fill.ForeColor.SchemeColor = 13
End Sub

This won't run. What am I overlooking?