X-Men Design and Effects

The filmmakers decided not to replicate the X-Men costumes as seen in the comic book. Stan Lee and Chris Claremont supported this decision. Claremont joked, "you can do that on a drawing, but when you put it on people it's disturbing!" Producer/co-writer Tom DeSanto had been supportive of using the blue and yellow color scheme of the comics, but once he saw tests of them, he declared, "No, that just doesn't work." Despite receiving positive feedback from various associates at Marvel Comics for the black costume design, fans on the internet still had negative emotions when X-Men was filming. To acknowledge the fan complaints, Singer added Cyclops' line "What would you prefer, yellow spandex?" – when Wolverine complains about wearing their uniforms – during filming. Singer noted that durable black leather made more sense for the X-Men to wear as protective clothing.
Wolverine's claws required a full silicone cast of Hugh Jackman's arm, and 700 versions for Jackman and his stunt doubles. It took nine hours to apply Rebecca Romijn's prosthetic makeup. She could not drink wine, use skin creams, or fly the day before filming, because it could have caused her body chemistry to change slightly, causing the 110 prosthetics applied to her skin fall off. Between takes, the makeup department kept Romijn isolated in a windowless room to ensure secrecy. Romijn reflected, "I had almost no contact with the rest of the cast; it was like I was making a different movie from everyone else. It was hell."
In the late 1990s, computer-generated imagery was becoming more commonly used. Singer visited the sets of Star Wars Episode I: The Phantom Menace and Titanic to understand practical and digital effects. Filming had started without a special effects company hired. Digital Domain, Cinesite, Kleiser-Walczak Construction, Hammerhead Production, Matte World Digital, CORE and POP were all hired in December 1999. Visual effects supervisor Mike Fink admitted to have been dissatisfied with his work on X-Men in 2003, despite nearly being nominated for an Academy Award.
Digital Domain's technical director Sean C. Cunningham and lead compositor Claas Henke morphed Bruce Davison into a liquid figure for Kelly's mutation scene. Cunningham said, "There were many digital layers: water without refraction, water with murkiness, skin with and without highlights, skin with goo in it. When rendered together, it took 39 hours per frame." They considered showing Kelly's internal organs during the transformation, "but that seemed too gruesome", according to Cunningham.