using System;

using System.Linq;

using System.Collections.Generic;

namespace Example

{

    static class ExtensionMethods

    {

        static public string GetStuffInsideParentheses_Old(this string input)

        {

            int i = input.IndexOf("(");

            int j = input.LastIndexOf(")");

            if (i == -1 || j == -1 || j < i) return null;

            return input.Substring(i+1, j-i-1);

        }

        static public IEnumerable<string> GetStuffInsideParentheses(this IEnumerable<char> input)

        {

            int levels = 0;

            var current = new Queue<char>();

            foreach (char c in input)

            {

                if (levels == 0)

                {

                    if (c == '(') levels++;

                    continue;

                }

                if (c == ')')

                {

                    levels--; 

                    if (levels == 0)

                    { 

                        yield return new string(current.ToArray()); 

                        current.Clear();

                        continue;

                    }

                }

                if (c == '(')

                {

                    levels++; 

                }

                current.Enqueue(c); 

            }

        }

    }

    public class Program

    {

        public static void Main()

        {

            var input = new []

            {

                "(blue,(hmmm) derp)", 

                "herpdediderp (orange,(hmm)) some other crap (red,hmm)"

            };

            foreach ( var s in input )

            {

                var output = s.GetStuffInsideParentheses();

                foreach ( var o in output )

                {

                    Console.WriteLine(o);

                }

                Console.WriteLine();

            }

        }

    }

}

​