Why do Mexicans call white people gringos?

Answer 1

Mexicans use 'Gringo' to denote Americans, not white people - Gringo does not extend to French or British people, for example. The word existed long before Mexico even became an independent country: it was used in Spain during the 18th century to denote foreign people who couldn't pronounce Spanish correctly. It is commonly accepted to be a variant of peregrino (peregrine) which changed to peregringo and then shortened to its current form, gringo. Depending on its context, it could be used as a pejorative, but most often than not, it just denotes an American national.

Answer 2

Güero [wher-o], güera [wher-a] if no nationality is known.