Eagle-eyed fans caught a glimpse of the Grey Hulk in promos for The Avengers: Age Of Ultron, but when the movie came out it turned out the Grey Goliath had been cut.
Now it's learned exactly why as VFX supervisor Christopher Townsend lets it be know the reasoning was to not confuse fans as there are different versions of Huk in the comics (and even different versions of the Grey Hulk with Joe Fixit and the Ultimate Hulk); via Screen Rant:
Yeah. What Joss wanted to do was he said, “I wanted to have a Hulk that’s this berserker Hulk.” Berserker Hulk was this Hulk that Hulks out, was what we had come up with on set. And then we sort of started talking about, “Well what are those extremes?” And ILM started playing with a deformed body with a deformed face with one eye larger than another. You know, like crooked teeth, and drooling, and red eyes, and all this kind of stuff.
Then we started playing with color and we started to de-saturate him and give him sort of red around his eyes and made him look strung-out heroin addict Hulk was the idea. Sort of like where he has totally lost it and he’s gone totally crazy. And then we gradually tended towards a grayer and grayer version till effectively we got gray Hulk.
We tried a few shots in the film with that sort of much grayer version. And then we’re thinking, “Will people confuse this with the gray Hulk from the comics? And is that a good thing or a bad thing?” Eventually, I think we backed off a little bit of that and made him greener so that…we didn’t want to confuse people in creating a new character, per se, in that way. So we ultimately backed off. But we had gone pretty extreme in the looks for him.