Sub colorize()
    Dim p As Paragraph, prev&, b As Boolean
    Application.ScreenUpdating = 0
    With CreateObject("vbscript.regexp")
        .Global = False: .Pattern = "^\d+\.\d+\s"
        For Each p In ThisDocument.Paragraphs
            If .test(p.Range.Text) Then
                If prev > 0 Then
                    p.Parent.Range(prev - 1, p.Previous.Range.End).HighlightColorIndex = IIf(b, 3, 7)
                End If
                prev = p.Range.Start + 1
                b = Not b
            ElseIf p.Next Is Nothing Then
                p.Parent.Range(prev - 1, p.Range.End).HighlightColorIndex = IIf(b, 3, 7)
            End If
        Next
    End With
    Application.ScreenUpdating = 1
End Sub

p.Parent.Range(prev - 1, p.Range.End).HighlightColorIndex = IIf(b, 3, 7)

p.Parent.Range(prev - 1, p.Range.End).HighlightColorIndex = IIf(b, 3, 7)

Sub colorize()
    Dim p As Paragraph, prev&, b As Boolean
    Application.ScreenUpdating = 0
    With CreateObject("vbscript.regexp")
        .Global = False: .Pattern = "^\d+\.\d+\s"
        For Each p In ThisDocument.Paragraphs
            If .test(p.Range.Text) Then
                If prev > 0 Then
                    p.Parent.Range(prev - 1, p.Previous.Range.End).HighlightColorIndex = IIf(b, 3, 7)
                End If
                prev = p.Range.Start + 1
                b = Not b
            ElseIf p.Next Is Nothing Then
                p.Parent.Range(prev - 1, p.Range.End).HighlightColorIndex = IIf(b, 3, 7)
            End If
        Next
    End With
    Application.ScreenUpdating = 1
End Sub

p.Parent.Range(prev - 1, p.Range.End).HighlightColorIndex = IIf(b, 3, 7)

Sub colorize()
          Dim p As Paragraph, prev&, b As Boolean
1         On Error GoTo colorize_Error

11        Application.ScreenUpdating = 0
21        With CreateObject("vbscript.regexp")
31            .Global = False: .Pattern = "^\d+\.\d+\s"
41            For Each p In ThisDocument.Paragraphs
51                If p.Next Is Nothing Then
61                    If .test(p.Range.Text) Then
71                        p.Range.HighlightColorIndex = IIf(b, 3, 7)
81                    ElseIf prev > 0 Then
91                        p.Parent.Range(prev - 1, p.Range.End).HighlightColorIndex = IIf(b, 3, 7)
101                   End If
111               ElseIf .test(p.Range.Text) Then
121                   If prev > 0 Then
131                       p.Parent.Range(prev - 1, p.Previous.Range.End).HighlightColorIndex = IIf(b, 3, 7)
141                   End If
151                   b = Not b
161                   prev = p.Range.Start + 1
171               End If
181           Next
191       End With
201       Application.ScreenUpdating = 1
211       On Error GoTo 0
221       Exit Sub
colorize_Error:
231       MsgBox "Error " & Err.Number & " (" & Err.Description & _
              ") in procedure colorize of VBA Document ThisDocument on line " & Erl & vbLf & _
              "paragraphs.count: " & Paragraphs.Count & ",  current paragraph: " & Range(0, _
              p.Range.End).Paragraphs.Count
End Sub