Bill Sienkiewicz - Legion, Mirage, Cypher and Warlock - New Mutants 27

Much as I would seriously LOVE for this to the original painting, it ain't.

It IS the colour guide used for a reprint, and that's about as close to the original as I'm ever likely to get, alas.

As well as being from the story arc that properly introduced Charles Xavier's son David Haller, soon to be better know to the world as the multiple personality with multiple powers Legion, this cover was also the first to feature Warlock and Cypher (in costume, no less), so has a small claim to fame, well, from my POV at least.