This braid is easy to learn and can be used for necklace cords, friendship bracelets or as a trim.
The one in the photos is made with standard embroidery floss. One strand each of blue and deep purple, three strands of grey. Start with strands that are about 33% longer than the finished braid length you need.
The only real trick to it is to make sure the group of three strands never twists together – keep them flat like a ribbon. If you flip the braid in the picture over, purple is the dominant color.