Two reds donāt always make a right?
Itās always seemed reasonably obvious to me that hair color isnāt an all-or-nothing thing, but then again Iāve owned dogs.
We tend to think of our hair as being all one single color, but really, just like most mammals, our hair comes in several different colors. I personally have curiously metallic silver hairs shot throughout my head hair (and no, Iām not just going gray, Iāve had them since I was a child), but theyāre so sparse in number that my dark brown hair conceals them almost all the time, despite their vibrant shine when the light catches them properly.
As for the brown hair, it comes in several shades, all dark, but with distinct differences. Some are glossier than the others, others are almost pure matte, and the middling textured hairs are for some reason the darkest of the three main types.
Then thereās the much darker and coarser body hairs, and among them I get the occasional wirey silver variant, and even rare stubby āredā stragglers and pale āwhiteā ghosts.
And of course separate from all of that is the colorizing effects of sun exposure or salt tinging that occur when I spend time at the beach.
Really though, ever since I was little I realized my hair wasnāt any single color. Just like my dogs with their multiple coats and multiple colors within each coat. Look at any well-furred mammal, really - none of them has merely one color of hair!
Two blue-eyed parents can have a hazel-eyed child.
Both my parents have dark brown hair and brown eyes, but three of their four children (including myself) have light brown/blonde hair and blue eyes. My wife has dark hair and hazel eyes, but the blonde hair/blue eyed genes stayed strong with our daughter.
If it was as simple as āthere are 3 hair genes - ginger, brown, blondeā, then all blondes would have exactly the same colour, similarly browns and gingers. (Give-or-take sun-bleaching or unnatural processes.) Oneās hair would be a constant colour all your life. But it isnāt. Iām ginger, but not as shockingly as in the picture. My dadās ginger, but could pass as light brown now.
Which, frankly, makes the brunette-guy-with-red-beard phenomenon make
a whole lot more sense.
I have dark brown hair (had, most people would say), and my beard matches exactly. However, if you look closely at the beard, instead of dark brown hairs, it has about an equal mix of black and bright red, the sum of which match the hair on (the sides of) my head.
Good example of what I am talking about!
The first generation is actually well explained by the classical (Mendelian) binary system of genetics*. Both your parents were heterozygous, with one dominant brown eyed gene and one recessive blue eyed gene. If they had a thousand or so children, 25% would be homozygous (2 brown eye genes) with brown eyes, 25% would be homozygous (2 blue eye genes) with blue eyes, and 50% would be heterozygous (1 brown 1 blue) with brown eyes. Only the dominant gene will be visibly expressed in a heterozygous child.
A very slight modification of Mendelās theory is required to explain the second generation. If you throw out the concept of a binary dominant/recessive and postulate a multi-value weighting system, you can suppose that hazel eyes are even more recessive than blue eyes, you and your wife are both homozygous, and it works fine. Your daughter is heterozygous with one blue and one hazel eye gene, the blue is more dominant and thus controlled the development of her eye color.
I figured the hazel/brown/blue non-binary weighting thing out as a child in the 1960s, and was publicly mocked for it by an elementary school teacher. Some of my attitudes towards science dogmas and science education can be explained by this experience. 
*Note: I do not believe Mendelās theory is any more valid than the phlogiston theory of heat. In reality the system not only has more than two weighting factors (DNA is not a base two system) but also people can carry more than two copies (the meiotic spindle can pull other genes out of cold storage). But, just like phlogiston works for most purposes, the classical explanation is a sufficient approximation for simple cases.
the pigment that causes red hair is likely present in many brunettes
Round here, we call them ācarriersā.
Oddly, for a a year or so as my dadās beard went from brown to grey, it went ginger. Looked bloody hilarious.
My ābrownā hair is ~30% colorless, 30% brownish, 20% red, 10% yellowish, 10% black. My beard is more distinctly evenly divided red/colorless/black (the blacks in the beard are now about 50% white).
Same here, bi-racial, kinky black hair, and a beard thatās half black hairs and half red.
A guy canāt be a brunette, surely? Heād be a brunet.
Brown hair with red beard here, just like my dad. Was blond when I was young. The recently arrived Daneel Jr appears to be a strawberry blond.
Our family is an interesting example thereof: my husband is a ācarrot topā with bright red hair and beard. I have auburn hair, reddish-brownish hair that changes with the seasons, though my mom had fox red hair in her day and my dad was a carrot top. My husband and I have three kids, a strawberry blond daughter, a fox red son, and a son with my brown/red hair. We all have pale skin, freckles, and had army green eyes until several years ago when my eyes turned light blue for no apparent reason. However, the one universal truth about all of our hair is that itās streaky: blond, brown, black, red in various shades, and white all are present in all of our hair to varying amounts. And we all have an inch wide circle of blond at the nape of our necks. I have always assumed that our hair is streaky for the same reason our skin is freckled: splotchy genes.
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