dot net controls are child controls of the form so you have to identify the name of the form first.

  For Each ctrl As Control In Page.FindControl("Form1").Controls
            If ctrl.GetType() Is GetType(TextBox) Then
                CType(ctrl, TextBox).Text = ""
            End If
        Next




For Each ctrl As Control In Page.FindControl("Form1").Controls
2:    If ctrl.GetType() Is GetType(TextBox) Then
3:        CType(ctrl, TextBox).Text = ""
4:    End If
5: Next 
\



For Each ctrl As Control In Page.FindControl("Form1").Controls
2:    If ctrl.GetType() Is GetType(TextBox) Then
3:        CType(ctrl, TextBox).ForeColor = Drawing.Color.Red
4:        CType(ctrl, TextBox).Text = "Text is RED"
5:    End If
6: Next