using System;
using System.Collections.Generic;
using System.Linq;

class Sample
{
    public string Value1 { get; set; }
    public string Value2 { get; set; }
    public override string ToString() {
        return Value1 + "/" + Value2;
    }
}

public class Test
{
	public static void Main()
	{
		var list = new List<Sample>() { 
            new Sample{ Value1 = "Apple", Value2="Red" },
            new Sample{ Value1 = "Banana", Value2="Yellow" },
            new Sample{ Value1 = "Lemon", Value2="Yellow" },
        };
        
        var s = new HashSet<string>();
        list = list.Where(n => s.Add(n.Value2)).ToList();
        
        foreach (var n in list) {
            Console.WriteLine(n);
        }
    }
}