The answer to the idiom is three old cold friends.
Three friends in cold years refer to pine, bamboo and plum. These three plants are named after their tenacious vitality in the cold winter. They are symbols of noble personality in China traditional culture and metaphors of loyalty and friendship.
The pattern of "Three Friends in the Cold Year" composed of pine, bamboo and plum is a common decorative theme in ancient vessels, costumes and buildings in China. Pine and bamboo don't shed leaves, and plum blossoms don't shed flowers, which means "clean and white", which is the ideal personality of ancient literati. At the same time, Three Friends in the Cold Year is still a common theme in Chinese painting, and paintings are often named after the "Three Friends Map".