From the creators' website:
In this demo, the text background of Wikipedia articles is colored according to a value of trust, computed from the reputation of the authors who contributed the text, as well as those who edited the text. ... Text on white background is trusted text; text on orange background is untrusted text. Intermediate gradations of orange indicate intermediate trust values. ...
We compute the reputation of Wikipedia authors according to how long their contributions last in the Wikipedia. Specifically, authors whose contributions are preserved, or built-upon, gain reputation; authors whose contributions are undone lose reputation.
We call this a content-driven reputation, since the reputation is computed automatically via text analysis. This contrasts with other reputation systems, such as those in use at Ebay, where buyer and seller reputations are computed on the basis of user-provided ratings. [Via|Link]