Sometime in the 1940s Texas government voted to allow Hispanics to attend public school, not as ??? but as Caucasians, which they have been for quite a few centuries.
Mexicans come from a variety of racial backgrounds. There are even black and Asian Mexicans. Most, of course, are a mix of white and (American) Indian:
https://en.wikipedia.org/wiki/Demographics_of_Mexico#Ethnic_groups
The ironic thing is that white Mexicans tend to dominate the upper reaches of Mexican society. Yet somehow when they come to the U.S. they get the same affirmative action benefits as their non-white compadres, whom they often seem to find some great new affinity with (now that it’s actually beneficial to them).