I've been thinking about this - especially after seeing the fair haired people around me looking at little off at time lately. Interesting your point about less tolerance to thermal.
My theory is that we are more impacted by everyday electrical sources - or rather their by-product dirty electricity, possible EMFs from towers, cell phones, microwaves etc. because of our fair skin.
I guess I basically get red face when I sit too close to my computer monitor on too bright a setting, etc. I can literally feel a burning sensation from some monitors when too large.
So we don't have the protection from the harm of this things like others have - the same way we are more likely to get burned from the sun.
If you can find it, there are references to Lyme doctors not treating patients until they clean their environments of these sources of dirty electricity, etc.
I think MS, diabetes, RA can all have electrical exposures as causal factors and seems like there is a lot of symptom overlap or combos out there - like a little MS and RA at once.
That is my theory that I've been wondering about.
Also, MS is more common in northern latitudes.
Definitely vit D matters - but in northern latitudes we have more dark days of winter and electricity use also.
I'm a redhead with a high pain tolerance and DO require more anesthesia as noted by the redheaded pain mangement doc who did my LP. His partner (brunette) did not use an adequate amount on the subsequent blood patch. My dentist is amazed at the about of novacaine it takes to numb my mouth.
I have read some articles pertaining to this in the past. In essence, the gene carrying hair color also carries pain receptors info or something of that nature as well as melanin. I have not read the links provided with this post however.
I have blue eyes of Northern European descent (English and Scottish). Grew up in South FL. Have been dx with endometriosis and surgery complications (infection and non-healing wound).
As for pain tolerance, 2 of my deliveries were natural WITH Pitocin drips to augment labor so pain isn't an issue unless you get me started on MS induced neuropathy in my legs which NOTHING seems to touch.
And, of course, hair color DOES NOT play a role in temperments. Red heads do not anger any easier than anyone else...especially if everyone would stop expecting us to get angry and then we wouldn't want to disappoint those of you with such high expectations of us :-).
Ren