@lucifargundam I'm pretty sure that's the entire basis of "ube" pastries.
"Ube cake is a traditional Filipino chiffon cake or sponge cake made with ube halaya (mashed purple yam). It is distinctively vividly purple in color, like most dishes made with ube in the Philippines."
https://en.m.wikipedia.org/wiki/Ube_cake
I don't recall ever had anything like this except for ice cream one time at Walmart... Though that was probably fake.
@LouisIngenthron
I wonder if you could make purple dye from yams...