I took a look at another walkthrough online and it says that the solution is:
I also read this advice in one walkthrough, which might be helpful:
Go to the Organ and play any note to start the Simon-Says puzzle. The Organ will play three notes, and you are to repeat them. HINT: Go to the Options menu and turn the music volume down to zero. Now you hear only the organ, and not the background music along with it. OTHER HINT: Instead of turning down the music, turn the Sound Effects all the way to zero. Now, you do NOT hear the organ play, rather you solve it by watching the keyboard. I found this to be the easiest method of all; particularly because I have a good ear, I do play the piano and organ, and the puzzle keyboard is unreal, and out of sequence. The disadvantage of this method, is that you will miss the 'Reward Sound' each time you complete a sequence; and the 'Reward Music' when you finish.