Yeah, it's still tough to tell because of Seviper's erratic movements in its attack animations, but it definitely is not a blue tongue anymore. Disappointing since the blue tongue was one of the coolest changes for shiny Seviper.
I didn't notice that any others had lost the shiny color on their tongue, though. It definitely seems intentional, in that case. I can't think of any limitations that would have caused them to not keep it, though. A shame, some shinies look amazing in X/Y, and others kind of lose their "wow" factor. Like Dusclops, I know you commented on that one.