Formula to add a blank row if 2 values differ

Try this

Option Explicit

Sub x()

    Dim rRng As Range
    Dim Rw As Long

    With Sheet1
        Set rRng = Range(.Cells(1, 1), .Cells(.Rows.Count, 1).End(xlUp))
        For Rw = rRng.Rows.Count To 1 Step -1
            If Rw = 1 Then Exit For
            If .Cells(Rw, 1).Value <> .Cells(Rw - 1, 1).Value Then
                .Cells(Rw, 1).EntireRow.Insert
                With .Cells(Rw, 1).Interior
                    .ColorIndex = 33
                    .Pattern = xlSolid
                End With
            End If
        Next Rw
    End With
End Sub