That was Tsukasa in the first episode who's shown unconscious, dumbass.THe black and white didnt symbolize a flashback, it symbolized the real world. IF you watch they have instances that were present of black and white, for example the crimson knight who was injured by tsukasa guardian in the beginning episodes.
The Black and White in .hack//SIGN represents ONE thing, and in order to understand that one thing, you have to understand Tsukasa. And I don't feel like explaining any of the .hack psychology anymore to anyone. I can't even properly explain why I hate UdeDen anymore.