Spoilers ahead for WandaVision Episode 8, "Previously On." In the penultimate episode of WandaVision, the witch Agatha Harkness leads Wanda Maximoff on a trip down memory lane in an attempt to figure out exactly how she created the sitcom bubble surrounding Westview. As Wanda relives some of the integral memories from her life, it's revealed that S.W.O.R.D. Director Hayward lied when he told Monica Rambeau that Wanda broke into S.W.O.R.D. headquarters and stole Vision's body in order to reanimate him. While Wanda did visit S.W.O.R.D. headquarters, she actually left the remnants of Vision's body behind after not being able to sense life within him. Instead, she created a new Vision using chaos magic.
The post-credits scene in Episode 8 shows that not only has S.W.O.R.D. been trying to figure out how to bring Vision back to life in order to use him as a weapon, but after channeling some of Wanda's energy, they've been successful. However, this reanimated Vision is distinctly different than the original version: he's entirely white.
There is precedent for this in the Marvel comics. During a storyline in the 1980s West Coast Avengers comics, "Vision Quest," Vision is captured and disassembled by some rogue government agents acting on behalf of time-traveling supervillain Immortus. The Avengers are ultimately able to retrieve Vision's body and rebuild him, but once he's reactivated, he's both colorless and lacks any of the emotion and humanity that was previously integral to his identity. In other words, white Vision is much more robotic than his original self. This change — in addition to the reabsorption of Vision and Wanda's twin sons into the demon Mephisto —unsurprisingly leads to the couple breaking up.
Though the circumstances that lead to the creation of this colorless Vision in WandaVision are very different than in the comics, it seems probable that this change in color is still meant to indicate that Vision has lost his humanity. Vision's color has always been tied to his life force and humanity within the MCU — after Thanos ripped the mind stone out of Vision's head in Avengers: Infinity War, all of the color drained from his body, leaving him a grey and lifeless shell.
It's not yet apparent what this development means for the season finale of WandaVision, but it seems likely that the series is building up to a confrontation between white Vision and the Vision that Wanda created within Westview. This puts a recent comment from Paul Bettany (the actor who plays Vision) about a WandaVision cameo from an actor that he has "longed to work with all of [his] life" into new context: it was actually an inside joke about Bettany getting to act opposite himself, portraying two different versions of Vision.