You could use code like:
Code:
Sub ShadeFields()
Dim Fld As Field
For Each Fld In ActiveDocument.Fields
With Fld
If .Type = wdFieldMergeField Then
With .Result.Shading
.Texture = wdTextureNone
.ForegroundPatternColor = wdColorAutomatic
.BackgroundPatternColor = wdColorAutomatic
End With
End If
End With
Next
End Sub
but if the aim includes displaying/hiding field shading, you might need to adjust that via File|Options|Advanced>Show document content>Field shading. That too could be changed via code.