Hey everyone. So, I know I posted a similar topic to this a long time ago (if you don't remember it, don't worry about it), but I figured I should rephrase it and share my own insights and gatherings about it.
So, before I start, I know this may sound like a rather odd thing to ask but this is something that has bothered me - and for those who play TESO and have Altmer, I'm sure there are those bothered by it as well or have been bothered by it before - for awhile now. My question is this: can a Altmer of purely Altmeri ancestry - meaning no Bosmer, Dunmer, Orsimer, or Human ancestry anywhere in their bloodline - have dark hair colors? Is it rare in pure-blooded Altmer, or are pure-bloods only capable of having fairer colors as Altmer in general are typically depicted as of late?
As for my gatherings about this, I had a look through each game to see how the Altmer are depicted. Arena shows them as capable of having black, gray, dark red, and (for men at least) dark brown hair with streaks of gray, and having dark gold to bronze-like skin. Then Daggerfall depicts them with a more fair complexion and their hair being red-orange, black, white, brown, and even a dark brown (or a dark red-brown, it's hard to tell really). Then there's Battlespire, which depicted both male and female Altmer with many black and dark brown hair colors and some of their more commonly seen white and blonde hair colors. Now we look at Morrowind - where a change in how Altmer are depicted begins. The Altmer shown - both the Nerevarine (if one chooses Altmer as there race, mind you), and those who moved to Morrowind or were based there if they're part of the Imperial Legion - are depicted with blonde, white, and even regular brown hair - the dark shades no longer present.
Oblivion is next - which takes place at the closing of the Third Era in the melting pot of Tamriel known as Cyrodiil. Many Altmer, once again, are shown with fair hair colors, yet some such as http://www.uesp.net/w/images/0/08/OB-npc-Caranya.jpg, http://www.uesp.net/w/images/e/ec/OB-npc-Areldur.jpg, http://www.uesp.net/w/images/d/d6/OB-npc-Hlidara_Mothril.jpg, and http://www.uesp.net/w/images/6/6e/OB-npc-Henantier.jpg are depicted with black and dark brown hair (though I refuse to count Mankar and his children). Then comes Skyrim and the Fourth Era. Altmer in the land of the Nords all seem to have only white, flaxen, blonde, auburn, and gray hair - not a single one seems to have brown, dark brown, dark red, or even black hair. The Thalmor are especially noticeable of this as both the common soldiers and high ranking members such as Elenwen and Ondolemar are shown to have blonde and white hair (whether this is to give a comparison to the Nazis of the real-world who were obsessed with 'racial purity' as some like to compare to the Thalmor to is intention or otherwise, who can say). Perhaps the reason the Altmer shown in Skyrim - both Thalmor-aligned and those unaligned with them - lack dark hair colors could be because those darker shades aren't as dominant in the genes of Altmer from Summerset/Alinor (assuming we can apply real-world genetics to Tamriel and racial phylogeny) - which could also be applied to the Altmer depicted in Morrowind. Although in the case of the Thalmor, it could very well be there way of promoting the 'unified ideal Mer' image to the Nords by sending 'poster Mer' - regarding their soldiers, high-ranking Justiciars, and representatives.
Finally, we look to TESO and the Second Era. Many Altmer of the Dominion sport white, blonde, gray, auburn, flaxen, and regular brown hair - however, there are a number in the Dominion who are shown to have dark brown, black-gray, and even black hair. http://www.uesp.net/w/images/3/30/ON-npc-Aldarch_Colaste.jpg, http://www.uesp.net/w/images/f/fd/ON-npc-Atalmo.jpg, http://www.uesp.net/w/images/e/ea/ON-npc-Canonreeve_Valano.jpg, http://www.uesp.net/w/images/7/7e/ON-npc-Coinclerk_Arawe.jpg, http://www.uesp.net/w/images/e/e2/ON-npc-Ocando.jpg, http://www.uesp.net/w/images/d/de/ON-npc-Ondendil.jpg, http://www.uesp.net/w/images/4/41/ON-npc-Palomir.jpg, http://www.uesp.net/w/images/b/b6/ON-npc-Sanessalmo.jpg, http://www.uesp.net/w/images/f/fc/ON-npc-Telenger_the_Artificer.jpg, and http://www.uesp.net/w/images/3/3b/ON-npc-Varustante.jpg. These Altmer are almost certainly pure-blooded Altmer. Some of these individuals are even members of the Veiled Heritance - Altmeri nationalist who oppose the Ayrenn's decisiion to align the Altmer with the Bosmer and Khajiit. Yet Altmer players have, as the darkest hair color they can obtain, a regular shade of brown - perhaps contributing to the idea that darker hair colors are rare yet possible and by not including these hair colors (though I'm still opposed to it) it keeps those hair colors rare and avoids a majority having black hair. I know, however, that Zenimax has claimed the choice of hair and eye color for each race Online is 'going by the lore' - however this is something I don't fully buy into, looking at the evidence presented, as well as the eye color options of Dunmer...
Anyways... If you managed to get through all of my possible madness (blame Sheogorath or obsession...), I thank you for bearing with me. And please, share your thoughts and your opinions on this matter - confirmation of pure-blooded Altmer being able to have dark hair or not will be reassuring in one way or another.