以下是一个使用C#比较两个属性列表并将差异添加到第三个列表的示例代码：

using System;
using System.Collections.Generic;

public class Property
{
    public string Name { get; set; }
    public string Value { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        List list1 = new List()
        {
            new Property { Name = "Name1", Value = "Value1" },
            new Property { Name = "Name2", Value = "Value2" },
            new Property { Name = "Name3", Value = "Value3" }
        };

        List list2 = new List()
        {
            new Property { Name = "Name1", Value = "Value1" },
            new Property { Name = "Name4", Value = "Value4" },
            new Property { Name = "Name5", Value = "Value5" }
        };

        List diffList = CompareLists(list1, list2);

        Console.WriteLine("Differences:");

        foreach (var property in diffList)
        {
            Console.WriteLine("Name: {0}, Value: {1}", property.Name, property.Value);
        }
    }

    static List CompareLists(List list1, List list2)
    {
        List diffList = new List();

        foreach (var property1 in list1)
        {
            bool found = false;

            foreach (var property2 in list2)
            {
                if (property1.Name == property2.Name && property1.Value == property2.Value)
                {
                    found = true;
                    break;
                }
            }

            if (!found)
            {
                diffList.Add(property1);
            }
        }

        return diffList;
    }
}

这个示例中，我们创建了一个Property类，它有两个属性Name和Value。然后我们创建了两个Property类的列表list1和list2。我们使用CompareLists函数比较这两个列表，并将差异添加到名为diffList的第三个列表中。最后，我们遍历diffList并打印差异。运行这个示例，我们会得到以下输出：

Differences:
Name: Name2, Value: Value2
Name: Name3, Value: Value3