The Hulk was originally grey.
Wipe the images of the muscled green giant tearing apart his shirt for a second and try to imagine him in a different hue. The reason for the change is surprisingly technical. Although all agreed on the grey color, when it came to printing the comics they found that his hue wasn’t always coming out consistently. Sometimes he would appear black, dark grey, or light grey. Ultimately, therefore, Stan Lee made the decision to change it. Seeing as green was a more printer-friendly color, Lee decided to change it for good. The grey version was not entirely scrapped though; he would eventually come back in later editions as the character of Joe Fixit.