I've been musing about a blog on redheads for some time. Red hair occurs naturally in about 1 – 2% of people, though those with northern or western European genes run higher, 2 – 6%. (Maybe higher yet among those of Celtic heritage.) Definitely a minority, but one that gets more buzz than other hair colors!
The red hair category covers a wide range of hues from dark auburn to strawberry blond and includes copper and carrot orange and usually comes with fair skin, light colored eyes, and a tendency to freckle. As Wikipedia says, "Cultural reactions have varied from ridicule to admiration; many common stereotypes exist regarding redheads and they are often portrayed as fiery-tempered."
On the negative side, there is the "red headed stepchild." I googled to get more information on what is probably a very old phrase. Apparently it can suggest an unfaithful wife who had an affair (the reference I found said that Irish postmen were often mentioned), and since the husband is the legal parent, he's stuck with "a redheaded stepchild." (It hardly seems fair to blame the child! But life is not fair.)
More broadly, the phrase refers to someone who stands out as different, and may be marginalized or unwanted. In Britain, redheads are sometimes called gingers, and not as a compliment. The Wikipedia article lists a number of examples of Britons being harassed and even physically attacked for being "gingers." (I've not seen this in the US; teasing, maybe, but low key. Possibly it's because the US has a more diverse population that Great Britain has traditionally had?