Costus 'Raspberry Yogurt' was named (I believe) by the late Mark Collins based on the purplish undersides to the leaves and the young new stems' coloration. It has since been identified as the species Costus vargasii. In 2013 I was in southern Peru and found the original collection site, confirming it is the same as the type collection for this species.
I have been growing it in large pots in my greenhouse over winter and it is a very dependable bloomer as well as a beautiful foliage plant. The stems form a tight spiral with dark green upper sides to the leaves and purple undersides. The red basal flowers are strikingly showy. Sometimes it will also flower terminally on the leafy stems.