using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var text = "(Today is a blue day) (Today is a good day) (Today is a BAD day) (Today is a green day) (Today is a blue day)";
		var matches = Regex.Matches(text, @"\((?>([^()]*\bBAD\b)?)[^()]*\)(?(1)(?!))")
    		.Cast<Match>()
    		.Select(x => x.Value)
    		.ToList();
        foreach (var m in matches)
        	Console.WriteLine(m);
	}
}