Dragon fruit won't win any awards for what it looks like on the outside, but the flesh makes a stunning cake and colourful icing. Some varieties have white flesh with black seeds. It's not very sweet, but has a nice texture. I used the juice to make a puree to swirl into the sponge cake mixture. Then I used more of it to make a pink icing for the cake.
Dragon fruit is also known as pitaya or pitahaya. It is an oval spiky, bright pink or yellow fruit of a cactus. Try to find pink-fleshed dragon fruit. White is more common, but the pink one gives the icing a nice pink hue.