1979's X-Men Annual #3 featured a cover by Frank Miller and Terry Austin.
However, a printing error resulted in the full cover art not appearing on the final cover.
As seen in this black and white version, there was a color overlay that was omitted when the final cover was printed.
However, while other blogs might be content to merely show you the original art, Citizen X is not! Through the magic of Photoshoppery, I have meticulously restored the cover to closer resemble what may have been the artist's original intentions. Gaze onward in amazement!
That is all for now, students of the X.