I saw these potatoes at the Zonottos market in Santa Cruz and at the local farmers markets but since it is winter, maybe you can request it at your local stores. Black potatoes!! (Purple Congo is the name of one variety of them.) They taste better than the standard russet but looks like a big red potato. They are a dark purple in color inside and out. When you mash them they turn to a nice lighter purple color. I have used them for just about every potato dish aside from curry. It is just something fun to twist your noodle around and scared my mother in law which is always a bonus for me.
Happy purple potato hunting! Here is a link to go look at what the color is like of these potatoes!