My skin is white but I am a full Mexican, should I have brown skin?

I honestly don't get it. Both my mom and dad have light skin like mine but they both were born in Mexico and there parents were Mexican as well. My Grandfather on mom side has brown skin as well as my grandmother has light skin. The same affect goes for my dad but his mom was brown and his dad was white. I... show more I honestly don't get it. Both my mom and dad have light skin like mine but they both were born in Mexico and there parents were Mexican as well. My Grandfather on mom side has brown skin as well as my grandmother has light skin. The same affect goes for my dad but his mom was brown and his dad was white. I would really appreciate if anybody can answer this question.

Note: My whole family is Mexican, there are no Mixes as far as I know.
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