The titles of the songs on the program for “Hong Lanpa s Music Festival: 100 Years of Korean Gagok” on Dec. 27 have a beguiling plainness, recalling natural scenes and sentiments about them that nearly everyone living in Korea is familiar with: “Barley Field,” “Magnolia Flower,” “Rock Pass,” “A Moonlit Night,” “Inside a Flower-shaped Cloud,” “Snow,” “Southern Village” and “Spring of my Hometown.”