using System;

using System.Collections.Generic;

using System.Linq;  

​

​

public class Program

{

    public static void Main()

    {

        var colorPallete = new string[]

        {

            "Red", "Green", "Blue"

        };

        var list = new List<MyModel>()

        {

            new MyModel() { ID = 1, Name = "model1", Class = "A", },

                new MyModel() { ID = 1, Name = "model11", Class = "AA", },

                new MyModel() { ID = 2, Name = "model2", Class = "B", },

                new MyModel() { ID = 3, Name = "model3", Class = "C", },                            

                new MyModel() { ID = 4, Name = "model4", Class = "D", },

                new MyModel() { ID = 5, Name = "model5", Class = "E", },            

        };

        //A. This code assigns null for unknown IDs

        //I.e. if (ID > 0 && ID < colorPallete.Length) then color will be picked from colorPallete[],

        //else it will be null

        list.ForEach(x => x.Color = colorPallete.ElementAtOrDefault(x.ID - 1));

        list.ForEach(x => Console.WriteLine(x));

        Console.WriteLine("-----------------------------------");

        //B. This code apply some default color for unknown IDs

        //I.e. if (ID > 0 && ID < colorPallete.Length) then color will be picked from colorPallete,

        //else it will be "DefaultColor"

        list.ForEach(x => x.Color = colorPallete.ElementAtOrDefault(x.ID - 1) ?? "DefaultColor");

        list.ForEach(x => Console.WriteLine(x));

        Console.WriteLine("-----------------------------------");

        //C. This code can assign the same color to models with different IDs, but models with identical IDs always will have identical color

        list.ForEach(x => x.Color = colorPallete.ElementAtOrDefault((x.ID - 1) % colorPallete.Length));

        list.ForEach(x => Console.WriteLine(x));                                        

    }

}

​

public class MyModel

{

    public int ID { get; set; }

    public string Class { get; set; }

    public string Name { get; set; }

    public string Color { get; set; }

    public override string ToString() { 

        return string.Format("ID={0};Color={1}", ID, Color); 

    }

}