The color is from purple yam:

You can read about it here 👉https://www.marthastewart.com/what-is-ube-8425552
It is popular in Hawaii, where I spent my early years.
It tastes like sweet potato, but blander.
Thank you for asking, @florian-glechner! I'm sure many are unfamiliar with the ingredient.
!BBH
!LADY
!PIZZA
