You may have noticed that Raidou's hair colour has changed now from what it was in part 1 -it used to be light coloured but now is coloured black. This of course is more useful for his sneak attack combination with Aoba but maybe there's more to it than a dye job? If you look at his sword you'll see that the tip of it is black but the whole blade is not -instead the black colour fades in. I think perhaps Raidou's techniques involve changing the colour of his hair/clothes/weapons so that he is harder to notice. Black is good for the combination with Aoba but not so good for other times because it's not a particularly natural colour. And if it were just for that surely his sword would be entirely black? I think he is a chameleon ninja to give a name to it because as we all know chameleons possess the ability to change colour according to their mood. It would be quite a nice little jutsu useful for stealth as well as attacks. Not as flashy as some but very sneaky which is just like a ninja.