This is a really interesting essay I found on an online forum a few years ago. I think it does well to illustrate the phenotypical variation in Northern Europeans, in this case it’s the British isles.
The first anthropologist to compile small survey studies of pigmentation (eye, skin and hair colour) of British peoples was John Beddoe (Races of Britain, 1885). However his sample sizes were only up to a hundred peoples from local areas across Wales and England. With no financial funding, Beddoe’s survey samples were always too restricted to draw concrete anthropological conclusions. It wasn’t until Tocher (1896) and Gray & Tocher (1901) that far more survey samples circulated.
Gray & Tocher 1901 (Scotland)
The first notable ethnological survey of the pigmentation (eye and hair colour) of the British was by John Gray in collaboration with the chemist and ethnologist James Fowler Tocher, which was funded by the Royal Society Government Grant Committee in 1901.   This study surveyed a sample of 502,155 Scottish school children (a high number of just over half a million). The results of hair colour showed that 26. 1% were blonde, 5. 3% were red, 42.1% were ”medium”, 25.2% dark brown  and 1.2% black. The ”medium” category included those of all brown shades that were not a darker brown (e.g. light or medium brown with possible tinges of red or blonde, such as chestnut or tawny). Of eyes, the results showed that 14.7% were blue, 30.3% non-blue ”light” coloured, 32.3% ”medium” and 22. 5% dark (incl. brown). The non-blue ”light” category included gray, or other non-blue ”light” shades (presumably green) and therefore if blue are added, light coloured eyes in total were precisely 45%. The ”medium” category included hazel and other intermediate colours.
In conclusion the Gray & Tocher 1901 study first showed that blondes in Scotland were a minority at only 26. 1%, with the majority (42. 1%) being ”medium” brown haired. Of eye colour only 14.7% were blue eyed, but with other ”light” eye colours added (e.g. light gray or green) the figure equates to 45%. The majority of the single eye colour category however were those with ”medium” hazel eyes (32.3%). After analysing the survey results, Gray concluded that because of the lack of fair haired blondes: ”we are driven to the conclusion that the pure Norse or Anglo-Saxon element in our population is by no means predominant.” (p. 380). The darkest haired region by population discovered was the south-western territory of Scotland, thus as Gray commentated: ”since in historical times, the Picts inhabited this region, this evidence points to the fact the Picts were a dark race” (p. 384). Coon (1939) has included another Tocher survey study of 7000 Scottish adult males and other sources to conclude that 38% of Scottish are dark brown haired, 42% ”medium to light brown” haired, 5% red haired and only 11% blonde (black was nearly non-existent). Beddoe calculated about 35% for dark hair in Scotland (excluding black hair) and noted that there was about an equal population of medium brown haired. Scottish children apparently are more fair haired, but darken with age (as in other populations). Therefore blondes in Scotland, as an average, as Beddoe and Coon have cautioned are lower, no more than 20%. The anthropological evidence is clear blonde or fair hair in Scotland has only even been a small minority, with medium and dark brown hair being the majority. All sources put redheads at precisely 5% and black hair at 0.5 – 1%.
Freire-Marreco 1909 (England)
Beddoe (1885, 1899) extensively wrote on the hair and eye colour of the Cornish and nearby south-western peoples of England, of which he concluded were the darkest haired.  Ripley (1899), Günther (1927) and Coon (1939) also all came to the conclusion that Cornwall had the highest population of black and dark brown haired individuals in Britain, only second to Wales. Beddoe, Günther and Lundmen have all written of a Semitic or Armenoid (”Hither-Asiatic”) racial admixture in Cornwall by Phoenicians, to account for the higher population of dark hair. Fleure (1925) also proposed a related eastern Mediterranid (or Anatolian) migration of ”Prospectors” to the Cornish and other regions across Britain. Others anthropologists have assumed that the Cornish people, especially because of their location, remained homogenous like the Welsh and retained a high degree of their original Mediterranid phenotype (Baker, 1974).
Only Beddoe had taken survey samples of the pigmentation of the English from the 1870’s. Some of these surveys of up to a hundred or so people from England can be found in his Races of Britain (1885). The first thorough anthropological survey however was undertaken by the female anthropologist Barbara Freire-Marreco in 1909.  591 school children from Surrey, from 7 schools, were surveyed on their hair and eye colour. The results showed that 47.9% were blonde, 36.9% light or medium brown, 2.4% red and 12.85% dark haired. The results of eye colours revealed that 15.7% had light blue, green or gray eyes and 21% dark brown, while the vast majority, 65%, had ”medium” or mixed classified as hazel or hazel-gray.
Coon’s Races of Europe (1939) contains several referenced studies of hair and eye colour of the English, only though in small surveyed numbers of a few thousand. As Coon has noted, the Gray & Tocher 1901 survey study (of just over 500,000) was one of a kind and there was never a survey that high conducted in England or Wales. However in summary it can be solidly confirmed that as Beddoe (1885), Coon (1939) and Lundmen (1977) have all recognised, England has sharply differing areas in regards to hair and eye colour. As noted the darkest populations in terms of hair are the Cornish. Although no figure has ever produced of the dark haired Cornish population, a pigmentation map in Coon (1939) shows this to be the darkest haired location in England, including the highest population of dark hair combined at 43%, while the majority medium brown. According to Beddoe (1885) less than 5% of Cornwall is blonde, while Coon (1939) believed it ”runs from 10 percent”, whatever the precise figure it is incredibly low as Wales.
Other regions in England that have a high population of dark hair are Buckinghamshire and Hertfordshire. Thomas Willis Shore in his Origin of the Anglo-Saxon race (1906) argued that Hertfordshire was predominantly brunette because it was settled by a Wendish (Slav) population who settled there with the Anglo-Saxons. Coon (1939) and other anthropologists have also discussed the re-emergence of an ”older Mediterranean element” in the Midlands of England, where pockets are considerably higher in dark hair. The highest population of blonde hair in England is found on the eastern coasts, particularly to the north. According to Coon (1939) the regions of the most intensive Saxon and Danish occupation have the largest proportion of blondes and the lowest proportion of dark hair (black hair being virtually non-existent). These areas include Lincolnshire, Norfolk, Suffolk and Yorkshire. Beddoe in a research paper has also noted of the higher amount of blondes in Lincolnshire. Coon maintained that ”dark brown hair accounts for 14 percent to 43 percent of the population in the different parts of England” while ”brown hair, a light-to-intermediate hue, ranges from 57 percent to 24 percent”. In all probability, based on the available anthropological surveys Coon’s conclusions draw closest to the truth, but he seems to have underestimated the population of dark hair in some more isolated areas of England, which Beddoe (1885) puts at a higher figure.
The majority of the English as all anthropological sources agree, including Lundmen (1977) are known to be ”medium” brown haired, a category including chestnut, tawny and all tinges of other colours, but these shades are not light or anywhere near true blonde. A plausible estimate based on Coon’s research would put this figure at around 50%. Blondes range as low as 5% in some areas (Coon, 1939). The average amount of blondes in England as a whole, comes to no more than 25% and Coon has claimed they are slightly larger a proportion than true brunettes. The highest areas of blondes are on the eastern coast (up to 47%) where the Saxon and Norse element is the strongest, but also in other parts of the country. The study Barbara Freire-Marreco (1909) showed 47.9% of Surrey children were blonde, one of the highest recorded figures of a single area. Adjacent regions decline in blondeness. Those with dark hair in England equate to around 20 – 22% (Beddoe, 1885). Black hair runs at only around 1%, and red hair from 2 – 4%, Beddoe claims 3%.
Of eye colours, Coon (1939) has noted that ”62 percent of English are called light eyed, and 34 percent dark eyed”. However as he clarified, his ”light eyed” category includes also ”light-mixed”, both of which are the majority over true light blue or gray eyes. Mixed is a hazel, and so ”light-mixed”, including green is obviously lighter. Beddoe (1885) and Freire-Marreco (1909) both classified ”mixed eyed” or ”medium eyed” as hazel or hazel-gray. Gray and Tocher’s ”non-blue light” category equates to Coon’s ”light-mixed” and includes all eye shades of light colour that are not light blue (or gray). To confuse things, Coon also notes that his dark eye category can include mixed eye types. It appears Coon placed hazel colours in the dark category, at 34%, which contrasts to Tocher’s study and classification scheme. Hazel eyes according to Coon must have been the majority over true dark, which places them around 20% and dark (incl. brown) at only at about 15%. According to Coon, there are more with light eyes in England than Scotland. Light-mixed types are around 45%. Since however no survey like the Gray and Tocher study was ever undertaken in England, there are less concrete figures on the eye shades of the English. In conclusion, based on the limited available evidence, the majority of England are ”light mixed” (light non-light blue) and hazel (medium) eyed, sharply differing in percentage in regions with a higher percentage of blue (true light) eyes than Scotland. Coon (1939) and Lundmen (1977) have both noted that ”fishermen of the North Sea coast have as much as 90 percent of light eyes” but that the Cornish are as low as 50%, again however as the ertminology is confusing these figures only include a small proportion of blue. True dark (brown) eyes are the minority in England and as a whole the rest of Britain however specific areas can have high dark eyed percentages, especially in certain areas of Cornwall.
Fleure 1916 (Wales)
Herbert John Fleure, a zoologist and anthropologist published his anthropological pigmentation study of several thousand surveyed Welsh men and woman in 1916, in direct response to Gray & Tocher’s 1901 study of the Scottish.  Far fewer people were however surveyed. Of 1852 men, 68. 9% had ”dark” hair (dark brown or black) while only 24% were ”light” haired (blonde or light/mixed brown). Of those with dark hair, 40. 1% had dark (brown) eyes while 28.8% had light (blue, gray, green) eyes. Of those with light hair (blonde or light/mixed brown), 20.5% had light (blue, gray, green) eyes, while only 3.5% dark (brown) eyes. Unfortunately Fleure’s dark category includes mixed eye shades, for example hazel, and it is very hard to calculate such a percentage but dark brown eyes appear at around 40 – 45% (see also Beddoe, 1885). Medium or mixed eyes hazel must be at a similar percentage, but light-mixed or true light (blue) eyes the extreme minority (Rhys, 1900). Fleure’s categories differ from Gray & Tocher’s since light or medium brown was included as ”light”, instead of ”medium”, the ”light” eye category also presumably included more intermediate colours. There is more data on hair colour. Blondes in Wales are far under 10% of the population, according to Beddoe, Rhys and other sources they are as low as 8%, or even as low as 5%. Coon (1939) also notes, ”only 8 per cent are fair in the English sense” and that ”dark brown predominates over medium brown”. Black hair is 15% (10% according to Coon, slightly higher according to Beddoe) and so dark brown at 55 % based on Fleure’s study, mixed-brown shades are considerably smaller in number, 25 – 30% based on Beddoe. Anthropologists have for a long time known that the Welsh have the highest population of dark haired individuals in Britain.  At Least two prominent Welsh areas are known to be between 70 – 89% dark haired (Beddoe, 1885; Lundmen, 1977). Coon (1939) drawing upon Beddoe (1885) also concluded that Wales is ”notably darker eyed” than the rest of Britain. According to Rhys (1900) the only blondes among the Welsh are a minority, aristocratic population connected to landowners reflecting an ancient distinction in physique among the classes because of Germanic (Aryan) blood (see also Baker, 1974).
The anthropological research concludes the following:
Medium brown haired: 40%
Dark brown haired: 35%
Blonde haired: 20%
Red haired: 5%
Black haired: 0.5 – 1%
Medium eyes (hazel): 32%
Light-mixed eyes (incl. green): 30 – 31%
Dark eyes (incl. brown): 22 %
Blue eyes: 15%
English: The majority of English are mixed or ”medium” brown haired. The dark brown haired population is less than in Scotland, except for certain regions, including most notably Cornwall and Hertfordshire. A plausible estimate of England’s ”medium” brown haired population is around 50%. In sharp contrast blondes or those with fair hair are known to be only 25% of the population as a whole, but are a higher population on the North Sea coast in historic Anglo-Saxon and Norse strongholds. Coon has noted that blondes are only a fraction more in number than true brunettes, or those with dark hair. Those with dark hair, lower than in Scotland, fall around 20 – 22% according to Beddoe (far higher in certain regions). Red hair runs from around 3%, while black 1%. Of eye colour the majority of English are ”light-mixed” eyed (45%) not true blue at around 20% ”mixed” (hazel) eyed, while the minority dark brown. Blue eyes appear to be in a higher number than Scotland, but still they are the minority at about 20%. However different regions massively differ and because of limited available anthropological survey results, estimates cannot be accurate on percentages as a whole but only be loosely estimated.
Medium brown haired: 50%
Blonde haired: 25%
Dark brown haired: 20 – 22%
Red hair: 3%
Black hair: 1%
Light-mixed eyes (incl. green): 45%
Medium eyes (hazel): 20%
Blue eyes: 20%
Dark eyes (incl. brown): 15%
Welsh: The Welsh are the darkest haired people in Britain. Fleure’s study shows two specific places in Wales up to 70 – 89% dark haired and overall they are 55% dark brown based on Fleure’s, Beddoe’s and Coon’s data put together. The rest of the population are ”medium” brown haired and the extreme minority blonde, under 10%, Coon states 8%, but it’s probably as low as 5%. There are far more people with black hair in Wales, at 10 – 15%. Red hair is put at about 2% by Beddoe, but Coon (1939) claims 5%. Of eye colour, the Welsh are the highest recorded population to have dark brown eyes, at 40 – 45%, followed by medium hazel. Light-mixed and light blue as the small minority.
Dark brown hair: 55%
Medium brown haired: 25 – 30%
Black hair: 10 – 15%
Blonde hair: 5%
Red hair: 2 – 5 %
Dark eyes (incl. brown): 40 – 45%
Medium eyes (hazel): 40%
Light-mixed eyes (incl. green): 10 – 15%
Blue eyes: 5%
 Memoir on the Pigmentation Survey of Scotland, John Gray, The Journal of the Royal Anthropological Institute of Great Britain and Ireland, Vol. 37, Jul. – Dec., 1907, pp. 375-401.
 Earlier Tocher had pioneered the first ever ethnological survey in 1896 of the pigmentation of 14,561 Scottish school children of East Aberdeenshire (Ethnographical Survey of School Children in Buchan, Trans. Buchan Field Club, vol. iv. pp.137-152).
 If all brunette shades are merged as a single catagory, then brown haired Scots equate to nearly 70%.
 These are the ”mean” results, other figures slightly vary (esp. for girls and boys).
 Ethnology of Cornwall, Paul Topinard and John Beddoe, The Journal of the Anthropological Institute of Great Britain and Ireland, Vol. 28, No. 3/4, 1899, pp. 328-329.
 Notes on the Hair and Eye Colour of 591 Children of School Age in Surrey, Barbara Freire-Marreco, Man, vol. 9, 1909, pp. 99-108.
 Geographical Distribution of Anthropological Types in Wales, H. J. Fleure and T. C. James, The Journal of the Royal Anthropological Institute of Great Britain and Ireland, vol. 46, 1916, pp. 35-153.
 Beddoe, 1885; Coon, 1939; Baker, 1974.