OK, so for whatever reason I got it into my head today to look up Zoroastrianism on Wikipedia. It led me to the concept of asha, the religion's core concept of goodness, which is usually translated with some variant of the phrase "truth, right(eousness), and order."
This is, it seems, where the three cardinal virtues "truth, light, and order" in Mask of Eternity come from. In interviews about Mask, Roberta Williams said she intended spirituality to be the core theme explored in the game.
A further Google search led me to discover that the phrase "Masks of Eternity" was used by scholar Joseph Campbell in his TV miniseries The Power of Myth (later largely transcribed in a book of the same name) as another name for "the Masks of God," his term for the varying interpretations of universal truth that are unique to each culture.
So... I guess Roberta took this metaphorical mask and made it into a literal mask. Interesting.
Roberta Williams has also said that she wanted Mask to be more inspired by the works of JRR Tolkien than were her previous games, which had frequently drawn on Walt Disney's movies for inspiration. Funny, given the general fan consensus (which I agree with) that KQ and Tolkien are two entirely different flavors of fantasy!