The darker the better. Many Spanish girls are also beautiful with lighter brown hair - even almost blonde, but it depends a lot on eye color and complexion. Red I don't like at all. But dark eyes with long black hair? Oh, yes!
Yuck, MRQUACK just described a tranny. It should be the oppostie way, if you're light skinned, which you're probably not, than go with light hair. If you're dark, meaning olive colour, go for something darker like redish browns or dark browns with golden brown highlights. But if you're blessed with a natural hair colour that suits you, keep it.
I don't think color is nearly as important as style. Go to a good stylist and get their advice.
I can't stand when I see spanish or black girls with Highlights..getting out of control with the blonde streaks. It looks sooooooooooooo fake. And WHY OH WHY do a lot of latina's draw on their eyebrows?!!!! that's sooooooooo unattractive. leave it natural and pretty girls. I Love when I see shiny dark chocolate hair on latinas...or black and shiny :) Nice! in case you are wondering..I am bi so I know what I like ;)