When Marvel's "Avengers: Age of Ultron" opens in theaters next month, a familiar set of iconic colors will be splashed across movie screens world-wide: The gamma ray-induced green of the Hulk, Iron Man's red and gold armor, and Captain America's red, white and blue uniform.

How the Avengers look today differs significantly from their appearance in classic comic-book versions, thanks to advancements in technology and a shift to a more cinematic aesthetic. As Marvel's characters started to appear in big-budget superhero films such as "X-Men" in 2000, the darker, muted colors of the movies began to creep into the look of the comics. Explore this shift in color palettes and browse more than 50 years of "Avengers" cover artwork below. Read more about this shift in color.