Tips: I used two different kind of sweet potatoes: Jewel and Japanese Sweet potatoes. Both are sometimes mislabeled as yams. Jewel sweet potatoes are the most common sweet potatoes and are easily identified by their orange skin and flesh. Japanese sweet potatoes have purple skin and butter-colored flesh. Be careful if you want to change the ratio of jewel versus japanese sweet potato. Cooked Japanese sweet potatoes are drier than “regular”sweet potatoes and therefore require less flour for the gnocchi to stick together.