I change my mind. I got a new batch of purple sweet potatoes today and these actually tasted pretty good! Used the candied yams method again, except I pre-boiled them this time. I think the ones i got the first time were definitely bad, as they had a much stronger (not so pleasant) odor. I also think boiling them is rather necessary. They're very sweet, but i can't say I prefer the flavor to the regular or asian yellow sweet potatoes. There's a slight hint of a grape/blueberry flavor (that I presume comes from the pigment), and it just feels odd coming from a... potato.
“Everybody has a secret world inside of them. All of the people of the world, I mean everybody. No matter how dull and boring they are on the outside, inside
them they've all got unimaginable, magnificent, wonderful, stupid, amazing worlds. Not just one world. Hundreds of them. Thousands maybe.” -Neil Gaiman