FlashOfSonic said: I'm wondering why Blue is dressed as Miku... and I bet he is too.
That is because 'Blue' is actually 'Green'- and although Miku could be considered blue, most consider her "Green"- since Kaito is true blue, and Miku is more seafoam-y.
It's a pun on their names- with the exception of Blue (the brunette girl). Green is dressed as the green Vocaloid: Miku, Red is dressed as Meiko: the red one, Yellow is dressed as Rin: the yellow Vocaloid.
Black Rock Shooter having really blue eyes could be why Blue (the brunette girl) is dressed as her. Honestly, Kaito or Kaiko would have made more sense to me.