Of course, the grey color could just be a variant - to sell more merchandise - but do we already have evidence of the Grey Hulk in The Avengers 2?
Look no futher than The Avengers 2 trailer as we see what appears to be a grey-colored Hulk fighting Hulkbuster Iron Man.
Internet speculation already has it that Mr. Fixit comes out as a result of Scarlet Witch casting a hex on the Hulk.
We do see Hulk's eyes appear to be red. Does grey follow? With Tony Stark matching the Hulk's strength with the Hulkbuster armor, does Grey Hulk outwit (as he is known to do in the comics) Iron Man to defeat him? Or is it just a coloring oddity?
"The Avengers: Age Of Ultron" hits May 1, 2015 directed by Joss Whedon starring Robert Downey Jr., Chris Evans, Chris Hemsworth, Scarlett Johansson, Mark Ruffalo, Jeremy Renner, Samuel L. Jackson, Elizabeth Olsen as Scarlet Witch, Aaron Taylor-Johnson as Quicksilver, Paul Bettany as Vision, with James Spader as Ultron.
When Tony Stark tries to jumpstart a dormant peacekeeping program, things go awry and Earth’s Mightiest Heroes, including Iron Man, Captain America, Thor, The Incredible Hulk, Black Widow and Hawkeye, are put to the ultimate test as the fate of the planet hangs in the balance. As the villainous Ultron emerges, it is up to The Avengers to stop him from enacting his terrible plans, and soon uneasy alliances and unexpected action pave the way for an epic and unique global adventure.
The Avengers 2 Trailer: