Murasaki sweet potatoes are characterized by their deep purple skin and creamy white flesh, as well as their extra starchy texture. 
They're sweet, through and through, with just a hint of chestnut flavor. They're a bit fluffy (again, like a russet) and a little less moist than traditional sweet potatoes and yams, but if you're a sweet potato fan, these will definitely satisfy that craving. 
Although they're sometimes labeled "Japanese sweet potatoes," Murasaki sweet potatoes were actually developed in Louisiana.