I have been a HUGE Jess fan ever since Never Been Kissed. Back then, I thought she was half black, as did a lot of my friends. In the late 90s and up until she got Dark Angel, she was very open about her Mexican heritage and seemed proud of it. But then her hair got lighter and lighter and the higher her profile got, the more adamant she was about being multiracial and such. I am not knocking her, but I just think it is more practical for her. She has admitted to having a hard time getting roles where she was not just seen as the exotic girl and that getting Sue Storm for her was huge.
On the other hand, Paula Patton, who I am not sure is or isn't biracial has a lot of drama going on on her IMDB board because there are people who refuse to think she could be all black-she must be half white.