The conventions for referring to hair color are tousled. Why is it that we refer to someone with light-colored hair as a blonde (and, rarely, a blond) but we call someone with red hair a redhead? Why are blonde and brunette spelled two ways?
Blond and its feminine form blonde, both from the Latin word blundus (“yellow”) by way of French, may have in turn come from a Frankish word that could be related to Old English blondan, “to mix,” which shares its origins with blend. Blond is usually employed as an adjective, the term as a noun for a man with blond hair, by contrast, is rare. Because blonds and blondes are more likely to be fair-skinned as well as fair-haired, the term is also associated with light complexion.
The presence of both masculine and feminine forms for blond/blonde and brunet/brunette is due to their French (and ultimately Latin) roots, as it were, as opposed to the Germanic origins of black and red, the words for the other major hair colors, which have a neutral form.
Normally, English might have jettisoned one gendered form for blond/blonde. However, the venerable theme in popular culture of the blonde-haired woman as more sexually attractive and available (as well as flighty, shallow, and dimwitted), as compared to females with hair of another color, has caused the noun form blonde and brunette to endure.
The numerous terms for variations in blond hair, not necessarily in order of darkness, include sandy, strawberry, and dirty. Towhead (the first syllable refers to its resemblance to tow, flax or hemp fibers used for twine or yarn) describes a person with yellowish and often unruly hair.
Brunet and brunette, from the gender-specific diminutives of the French brun (“brown”), mean “brown haired.” (Brun and its diminutives originally also referred to a dark complexion.) As with blond and blonde, the male form is rarely used on its own as a noun, though the masculine and feminine variations persist probably because of the same double standard in association of hair color with female sexuality and with personality characteristics as mentioned in reference to blondes above. (Dark-haired women are stereotyped as serious, sophisticated, and capable.) Words for shades of brown hair, from darkest to lightest, are brunet/brunette, chestnut, walnut (the last two as compared to colors of the respective nuts), golden, and ash.
Redhead is yet another term for hair color used as a noun; in contrast to the colors mentioned above, it is not gender specific, though as blonde and brunette are much more common in usage than blond and brunet, it is more likely to refer to a woman than a man.
Variations in red hair, listed in alphabetical order rather than according to depth of color, include auburn, copper, ginger, and orange. (Auburn derives ultimately from the Latin word albus, meaning “white,” but thanks to the influence of brun, the French spelling — auborne — changed, as did the meaning, to “reddish brown.”) The prevailing — and long-standing — cultural stereotype about redheads is that they are hot tempered; the hair color has also been associated with a high libido.
Alone among descriptions of people with general hair tones, a black-haired person is never referred to by the word black alone.
Hair-color categories are arbitrary — strawberry blond is sometimes considered a type of red hair, and auburn might be classified as a type of brown hair — though a system called the Fischer-Saller scale, devised for anthropological and medical classification, assigns alphabetical letters and roman numerals to various grades of hair color.