It’s one of pop culture’s most iconic transformations; from scientist Bruce Banner to the Incredible Hulk, a Jekyll & Hyde meets Boris Karloff’s Frankenstein story for the atomic age. Banner's rage-fueled transformation is a simple idea that ended up being profoundly relatable. But why does he have green skin?
The obvious answer is that - generally speaking - in popular media radioactivity is portrayed as having a green glow and Bruce Banner transforms into the Hulk after being caught in what should’ve been a lethal blast of Gamma rays. The comics themselves have offered other answers, from Amadeus Cho's theory that the Hulk's color is a fresh full-body bruise to the current run of The Immortal Hulk, which has suggested gamma radiation connects humans to a supernatural force called the Green Door. All of this is great food for thought, but the real answer is a lot less scientific and a lot more workaday than you might have thought.
When the character was first introduced in the pages of The Incredible Hulk #1 (1962), by Stan Lee and Jack Kirby, he wasn’t the now instantly recognizable purple-panted, green Goliath fans know and love today. Instead, he was a gray-skinned, blue-pants-wearing monster. Stan Lee chose this original color because he found it mysterious and spooky, and felt it would match the tone he wanted for the character.
However, back in the 1960s, printing technology being what it was, the color grey was impossible to print consistently. From panel to panel and page to page, the Hulk’s skin color would jarringly shift from lighter to darker - sometimes nearly jet black. Something had to be done, so the decision to change the color was made quickly, and the Hulk appeared in the easier to print green in the second issue.
Of course, it wasn’t just that the color was easier to print, but that it wasn’t readily associated with any other popular comic book characters at the time. The Hulk couldn’t have been orange, for example, because the Fantastic Four - a smash hit that had come out only months earlier - already had an orange-tinted heavy-hitter: Ben Grimm’s the Thing. Ironically, Stan Lee would go on to say that the change in color actually made his life easier as a writer. In interviews, Lee confessed his love for advertising and catch-phrases and having a green Incredible Hulk meant he could give the character fun nicknames like the “Jolly Green Giant” and “The Green Goliath.”
So, why is the Hulk green? In comics canon, that's simply the physical effect of gamma radiation, turning the Hulk's skin, Doc Samson's hair, and She-Hulk's nails green with stored gamma energy. There may be a more metaphysical answer yet to unfold involving the mysterious Green Door, but that recent addition to Hulk's canon will have less to do with the original truth, which is that the Incredible Hulk was turned green by the practicalities of printing and Stan Lee's excellent instinct for marketing.