Whats wrong with my skin?

Okay I'm native american and Jamaican, well for some reason everybody tells me my skin looks like I'm always dehydrated or that off black like a dead person (I drink lots all day, work out an am healthy). Also on my arms an face I have faint bloches. My brother is the same thing as me but is darker and perfect skin. WHY IS THIS and how can I fix my skin....ADVICE