Many seasoned and cultured interstellar travellers can attest to the fact that there are always beings that stick out in a crowd more than others. Usually the question of which beings stick out most depends on one's locale, and Earth is no different. Earth's creatures have various ways of attracting attention: making a great deal of noise, or being the strongest or fastest among a population among many species; evolving tastefully outlandish plumage among masculine avian societies; or indeed simply possessing an odd physical trait, as many marine creatures have done.
The dominant human population is no different. There seems to be an innate consensus that one should try to be "individual", and indeed many humans strive to distinguish themselves as much as possible by adopting various modes of dress, habits of exercise, and attempting various stunts and actions. Some, however, just stand out naturally. Among many segments of population, those possessing red hair are most naturally noticeable. Some of those possessing more common hair pigmentation attempt to replicate this coppery pigmentation, but unless one knows a very good cosmetologist it is next to impossible to synthetically achieve this remarkable color.
In other parts of the galaxy where beings possess red hair, colloquially known as "redheads", genetic scientists have theorized that this vibrant hair color is Nature's way of making up for a common lack in skin pigmentation. Redheads are known for their very fair complexion, which means they must be conscientious about sun exposure.
Often because of these two distinguishing characteristics, among others, some pockets of the population look down upon their coppery counterparts. Sometimes referring to them as "gingers", these pockets avoid redheads and occasionally compare their hair to root vegetables. Extreme sects even speculate this red pigmentation mark gingers as "soulless". This latter point, as scientists in the Eastern Mid-Galaxy have recently discovered, is completely bunk in humanoid species. Some redheads are put off by the term "ginger" when used in a derogatory sense, which is understandable. Many, however, prefer to see the term in a positive manner; to most it's merely a term to describe their hair color alone.
There is very little explanation as to how red hair came to Earth; among itself the human population agrees that it was a gene mutation, but when compared to galactic genetic history, and indeed genetic records in neighboring galaxies, this explanation is hardly sufficient. The most agreed upon explanation among the members of the Galactic Genetics Group, History division is that those aboard the legendary Disappearing Dories of Retz (which vanished in Sector ZZ9-Plural Z Alpha during a ill-fated pan-galactic exploration journey a few millennia ago) marooned in the northern hemisphere of the planet Earth, most notably on some northerly islands (one of which was predominantly green). The division further explains that this makes logical sense, because the people of Retz not only possess the necessary pigmentation, but also similar dispositions and tendencies to the people in the presumed areas.