You guys act like they changed the look. They didn't change a thing. Check out the original Comic Con teaser poster. He has WHITE EYES, lol. That was always going to happen.
Also Apocalypse was never purple. Bad lighting can make a reflective blue, look purple, and theres a big difference concerning a BTS photo, a magazine cover and an actual still from the film. Almost every time an X-men character appears on a magazine cover, or BTS photo is not representative of their final look/feel on film. Though the design may be the same, the context in which it appears matters the most.
Also the Magazine cover shows him at at least 7 ft. If you look closely his hands are on Magneto and Psylockes shoulders. Must have missed that all these months?