Sub ColorRows()
    Dim cell As Range, color1 As Variant, color2 As Variant, rowColor As Variant
    color1 = vbCyan
    color2 = vbWhite
    With ActiveSheet
        For Each cell In .Range("A4:A" & .Cells(Rows.Count, 1).End(xlUp).Row)
            If cell.Font.Bold Then
                rowColor = IIf(rowColor = color1, color2, color1)
            End If
            cell.EntireRow.Interior.Color = rowColor
        Next
    End With
End Sub