Since it is the title of an artwork, the owners of the artwork may proclaim the “official” English translation for the whole world. (For instance, the Chicago hit single “Colour My World” has the Brit “u” even though it is an American group, and even on the Columbia release stateside. Same with Del Shannon’s “Colour Flashing Hair”)
That said, Wikipedia agrees with you on the art in question.
https://en.wikipedia.org/wiki/The_Last_Judgment_(Michelangelo)
So as far as I know, you get the win on this one.