On a beautiful summer day, you don’t need much of an excuse to dine outdoors — especially if you’ve got a garden, patio or deck surrounded by greenery. “It’s more relaxed when you’re outside, so the way you entertain tends to be more casual,” said Young Huh, an interior designer based in New York. “It’s a little more fun and a little less fussy. I focus more on bright colors and creating a joyful feeling.” During the summer, Ms. Huh and her husband, Joon-Yeung Huh, a lawyer, entertain almost every weekend at their 19th-century house in Hyde Park, N.Y. And…