I know that the original Hulk was originally supposed to be grey, and real life printing issues and decisions caused him to eventually be portrayed as green (and then grey again).

However, is there any in-universe/canon explanation as to why, in addition to causing extreme size and strength increase, the gamma-radiation that turned Bruce Banner into the Hulk also caused his skin color to change?

I realize that the origins of the decisions regarding the color of his skin during his change are rooted in the original comic, but any "officially sanctioned" source that gives an in-universe explanation would be welcome.

  • I think that person was looking for a more scientific reason. Like the green being the primative core of mitocondria energy production. But the real question is where does the Hulk get his mass and energy/ strength from?
    – user15885
    Commented Jul 10, 2013 at 11:33
  • @SighinTest Actually this has been answerered here :)
    – Kalissar
    Commented Jul 10, 2013 at 12:40

3 Answers 3


I'm not sure if this article would best answer this question for you but according to marvel the grey and green hulk's were brought about by different stimuli. The grey Hulk came from when Bruce was first transforming and could only transform at night. The green Hulk came from when Bruce's adrenaline caused him to change.


The actual reason seems to be a bit more technical (and not really related to the plot, although they later do explain the color-change in universe). From Wikipedia:

In the debut, Lee chose gray for the Hulk because he wanted a color that did not suggest any particular ethnic group. Colorist Stan Goldberg, however, had problems with the gray coloring, resulting in different shades of gray, and even green, in the issue. After seeing the first published issue, Lee chose to change the skin color to green.

  • 1
    I have a trade paperback that reprints the first issue, but they have recolored the Hulk from gray to green. Also several What If? comics revisit the events of the first issue and he is green then too. This highlights the fact that there isn't an in-universe reason, Hulk has been retconned to be green from the start. Commented May 24, 2016 at 4:55
  • 2
    And as Stan liked to do, he'd change the story to suit the audience. In Origins of Marvel Comics, he blamed the color changes on the printer, then explained that he then went to green cause there weren't too many other green characters in comics at the time. Some years later, on ABC's "Kids are People Too" he skipped the printing issue altogether, and made it as if he'd chosen green from the first moment. It was Peter David that "Brought back" the gray hulk, under the name of Joe Fixit. Commented Dec 29, 2019 at 20:05

My possible explanation is that it's the result of the species he tested with. Or maybe the exceeded exposure to Gamma radiation may also be reason. The only problem with that theory is why is he not green when he is Bruce Banner? Is it because of the factor that is responsible for huge mass conversion that has managed to change his body colour as well?

  • "the species he tested with"? We are not talking about She-Hulk here :)
    – Eureka
    Commented Feb 2, 2014 at 10:02
  • More seriously, welcome among us! Do you have any elements to support this "exceeded exposure" theory?
    – Eureka
    Commented Feb 2, 2014 at 10:03

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