You just have to loop through the slides in the presentation, like:

Sub changedcolor()
Dim hshp As Shape
Dim osld As Slide
For Each osld In ActivePresentation.Slides
    For Each hshp In osld.Shapes
        With hshp
            If .Name Like "Google*" Then
                .Fill.ForeColor.RGB = RGB(50, 50, 50)
                .Fill.Solid
            End If
        End With
    Next hshp
Next osld
End Sub
edit: code formatting