Well it actually doesn't change the tint. How it works is the actual tint is applied to the glass. There's a special film (electrochromic film) applied that can be clear or milky white (depending on voltage applied).

So when the special film is clear you can see through the tint. When opaque it looks mirrored (special film + tint). So, it does NOT change the tint level - only whether you can see through it or not.

Of course, I could be wrong and maybe there are different applications.