"as are most Mexicans......."
The vast majority of Mexicans are not white. They're Mestizos of mixed Indian and Spanish blood. There are more pure blood Indian Mexicans than pure white Mexicans.
Did you see some of the signs the demonstrators in L.A. carried that read "We are not Latinos and we're not Hispanics - We're Mexicans" meaning as in Aztecs.
Probably the over-simplified but mostly spot-on "litmus" test would be whether or not one "blushes" or "sunburns" easily. I do both. In the major metro areas of Mexico, such as Mexico City, and in places with more established hispanic populations, such as San Antonio, there are more folks that look like me, Eva Longoria (from Desperate Housewives), Constance whatever-her-name-is (from George Lopez), and Henry Bonilla, than there are folks that look like the guy holding the sign on my profile page (the more Indian example) or Princess Stephanie (the more Spanish example, although I don't think she's Spanish). However, when you get into the rural areas of Mexico, the Indian type and the Princess Stephanie type extremes are frequently seen.