Red Hulk's different color comes from the way he got his powers, while also indicating his different powers to the original green Hulk.

While Harrison Ford’s Red Hulk has cemented itself as one of the standout features of Captain America 4, the character interestingly did not have any dialogue in the film. The villainous, rage-fueled monster only made a brief appearance in Captain America: Brave New World but failed to deliver any lines in his big-screen debut.

Brave New World and why it felt so strange to me. It was meant to be an espionage thriller (spoilers follow) in the vein of The Winter Soldier, and yet there was no real conspiracy (no traitors, just a guy randomly mind-controlling people) and a twist that was given away in the first trailer (Ross turning into Red Hulk in the Rose Garden).