Who are my white decedents and why didn't they leave a trace.. besides there looks?

im mexican american but im light skin, i have light brown eyes and brown hair.. but there are things that dnt look so ''mexican'' to mexicans from mexico when i visit mexico.. no one knows my native american side, but we do know we come from Spaniards, especially from my moms side.. my moms mom and sisters had colored eyes( some of there fathers had blue eyes too) and my great great granddad had blue eyes blond hair from durango mexico but im curious to know from wat ppl we come from.. its kinda sad that we have so many clues but very lil knowledge.. is there some kind of gene testing or how much percentage i am of white and native indian or something plz help