Grew these from cutting a few sweet potatoes from the shop, placing in a glass until sprouted, then twisted out each sprout and planted. The purple outside/white inside was the sweetest. Other ones include purple inside and out (less flavour and sometimes fibrous) and the boring orange one.
Update on 2020-08-16:
Harvest day! Time to weed the garden, might as well see what we can find. And here we go, quite a few decent sized sweet potatoes, mostly purple/purple but some are the orange variety too.