using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var rand = new Random();

        for (int i = 0; i < 20; i++)

        {

            Colors randomColor = rand.GetRandomEnum<Colors>(new List<Colors> {Colors.White, Colors.Black});

            Console.WriteLine(randomColor);

        }       

    }

}

​

public enum Colors

{

    Red = 0,

    Blue = 1,

    Green = 5,

    Yellow = 3,

    Black = 2,

    White = 6

}

​

public static class ExtensionMethods {

    public static TEnum GetRandomEnum<TEnum>(this Random rand, IEnumerable<TEnum> excludedValues)

    {

        var type = typeof(TEnum);

        if (!type.IsEnum)

            throw new ArgumentException("Not an enum type");

        var values = Enum.GetValues(type).Cast<TEnum>();

        if (excludedValues != null && excludedValues.Any())

            values = values.Except(excludedValues); 

        //create a random index for each possible Enum value 

        //will never be out of bounds because it NextDouble returns a value

        //between 0 (inclusive) and 1 (exclusive)  or [0, 1)

        int randomIndex = (int) (rand.NextDouble() * values.Count());

        return values.ElementAt(randomIndex);

    }   

}