using System;

using System.Collections.Generic;

​

public static class Program

{

    static void Main()

    {

        var source = new string[]

        {

            "Red", "red", "blue", "green", "green", "red", "red", "yellow",

            "WHITE", "white", "red", "white", "white"

        };

        var result = source.ExcludeConsecutiveDuplicates(StringComparer.OrdinalIgnoreCase);

        Console.WriteLine($"Result: {String.Join(", ", result)}");

    }

​

    public static IEnumerable<TSource> ExcludeConsecutiveDuplicates<TSource>(

        this IEnumerable<TSource> source, IEqualityComparer<TSource> comparer = null)

    {

        ArgumentNullException.ThrowIfNull(source);

        comparer ??= EqualityComparer<TSource>.Default;

        (TSource Value, bool HasValue) previous = default;

        foreach (var item in source)

        {

            bool isDuplicate = previous.HasValue && comparer.Equals(previous.Value, item);

            if (!isDuplicate) yield return item;

            previous = (item, true);

        }

    }

}

​