Well, on the internet, it says that Aeonium 'Big Bang' is a variegated plant. From my understanding Variegated plants have parts of their leaves with no chlorophyll.
Aeonium 'Big Bang' seem to be a plant with certain spots of its leaves that lack Anthocyanins. It doesn't seem like variegation
It fits the (botanical) dictionary definition of variegation. As you have observed, the color that is lost is purple, not green. So presumably it's not a defect in chloroplasts or chlorophyll, but something else at play.