The hologram's name is Hatsune Miku, and she is a product of Yamaha's "Vocaloid Synthesizing Technology." Somewhere, deep down, there is a real human vocal recording...but Miku herself is not real and her "concerts" are composed of pre-programmed light and sound. Naturally, she has blue hair. You gotta have blue hair!
Her computerized voice is actually based on a cartoon voice actor's voice. Real singers weren't interested in having their voices being used for this. We haven't the slightest idea how this sort of show ever became popular, and we fear for the future of the music industry.