Granted, the blonde hair is a short step away from the white hair that Slade frequently has in the comics, but going blue would be a bit too far.
Luckily for Manganiello, it’s a lot easier to color dye hair blue working from a blonde template rather than his usual dark hair, so good on him for trying something new.
Unless Zack Snyder decided to change up Slade Wilson’s physical appearance as part of the tweaks he’s been making for his version of Justice League, it’s probably safe to assume that Joe Manganiello has finished filming his scenes.