Why am i darker then most of my family ?

so, before you read anything else and get the misconceptions that i'm racist or look down upon a certain ethnicity. i don't. so my question is i get mistaken for mexican frequently, and i don't see nothing bad about it. i actually sometimes wish i was mexican because they always have things going on like quinceneras and stuff and many friends i have are mexican and their parents are really fun to be around. but my dad's parents are that his dad is from spain (murcia, to be exact) and his mom was from sicily (palermo). they immigrated to jalisco in mexico in the early 60's and didn't migrate to the states because they said there was just too much sh!t going on at the time. so my dad and his siblings were born and raised in mexico but were of spaniard and italian descent. and on my mom's side her mom was puerto rican and her dad was white (german). but my question is that why am i darker then most of my family (except my puerto rican side) my little sister who is 6; has light brown hair, skin the same shade's as selena gomez's and hazel eyes. and my brother who is 12 or 13; i'm not really sure lol has olivish skin, light brown hair and green eyes. both my parents are in olivish skin category. i was born with really light brown hair but for some reason my hair turned a slighty darker to almost dark brown, and i have light brown eyes. here's a picture of when i was a baby - a href="http://i55.tinypic.com/2vba8sn.jpg" rel="nofollow"http://i55.tinypic.com/2vba8sn.jpg/a - and now i'm pretty tan but not as dark as a traditional mexican. i have like a goldish brown tan, people say i fake and bake which i've never done in my life! (i'm scared to do so after watching that one movie where the two girls die in the tanning beds) lmfao. but why am i tan? i mean the lightest i ever got was an olivish tan when i lived more upstate (washington) and was still pretty tan. is it just that i got the puertorican genes more then my siblings? i do know that my great grandparents on my mom's side were really tan. i don't even know if this made any sense whatsoever but if you do understand what i mean, please give me a mature and honest answer. and yes i do know that spaniards and italians are light, i've been to both places plenty of times and my sicilian family says i fit right in because they're all slightly tanner the italians up north.