Beans can be found in a variety of hues at this time of year. In addition to the more well-known green beans, this family of legumes known as snap beans, appear in yellow and white and the alliterative Dragon’s Tongue bean looks like it’s been licked with purple flames. One of my favorite snap beans is the Royal Burgundy, a deep violet that almost looks black.
Royal Burgundy’s can be a bit tough, especially if picked when mature. This makes them great for pickling or canning but you can eat them raw (if you have strong guts and generally do well with raw foods) or you can do a quick blanch to tenderize them. It is through cooking the Royal Burgundy that I first fell in love with them. I put them into boiling water and turned my back for a few seconds. When I turned back to the pot, Holy Technicolor Beans, Batman! These heirloom legumes were no longer a deep purple. They were green!
Like purple cauliflower and purple cabbage, the hue of the Royal Burgundy bean fades when exposed to environments that are less acidic than the soil where it was born, like boiling water or heated oil.  It’s a fun trick to use with kids and may even get them to eat these high-protein, high fiber, Vitamin C-rich veggies. 
Royal Burgundy’s are not available everywhere but I recommend any kind of snap bean to clients who are trying to be healthier because beans are nutritious and filling. They are great if you are trying to increase your vegetable intake but struggling to feel full. Snap beans work with many restricted diets but their uses are versatile: Add a delicious crunch to salads, dip in hummus at a picnic, sauté with garlic or, after blanching make them, make them French-style tossed with a light mustard vinaigrette and fresh dill. Because they are so hearty, they stand up well to bold-flavored Asian applications such as a rich coconut curry or a wok stir-fry with sesame oil and sesame seeds. Anyway you toss them… Enjoy!
 “Why Do Purple Beans Turn Green after Cooking.” from Garden Betty: Diary of a Dirty Girl blog.
 Rahi Seed Bank’s description of Royal Burgundy beans.