Black History Month Ireland, why?

Yes and no Wren, rather the reasons are still up in the air. Take Tasmanian peoples, they were very dark skinned yet they lived in a (southern) temperate climate. Asians got a different set of genes that gave them lighter skin(and better ones too as unlike pale indo Europeans they suffer from skin cancers at about the same rate as darker Africans and their skin is more resistant to age related skin damage). One theory goes that it was farming that led to paler skin. Hunter gatherer diets tend to be far more varied and nutritious compared to farming diets and have more vitamin D available. So the idea goes that when we started farming in more temporate climes where the diet wasn't enough to cover our vit D needs lighter skin took over. Even this is conjecture as where farming first started the fertile crescent is extremely strong in sunlight and the peoples are much paler than Africans.

The ancestors of Irish people today aren't the original hunter gatherers whose genetic legacy is almost entirely gone. They were replaced by farmers from the near east as were most of Europe's populations. Even Basques have a genetic disconnect between modern people and Basques of 5000 years ago. It looks like Neandertals were pale, but again there's a lot of conjecture going on because there isn't a "gene for colour", there's a suite of them and the skin tone of earlier peoples is not nearly the clearcut given that many of these reconstructions claim. For example the guys who did the Cheddar Gorge dark skinned early Briton are also the same guys who reconstructed a Neandertal woman with mousey reddish blonde hair and light eyes.

Impressive but more art than science.

There's a problem with such reconstructions; they pretty much always reflect the current wider "fashions", even politics, with often very shaky science. Look at reconstructions of Neandertals over the last hundred years. They start off as crooked "cavemen" with clubs, hairy and brutish, subhuman sports of god and stay that way for decades. Then when research showed non Africans have their DNA, so we got busy with each other around the campfire, it's remarkable, or not, how modern human looking they then become...

Contrary to the whole "Dublin second city of empire" thing we hear; that was an earlier period and by the late 19th century(and after one of the worst famines in modern European times) Dublin and Ireland was more a backwater and one that had one of the most populous slums in western Europe. It was not a place to "go west young man" to seek one's fortune. It was about the least industrialised city in the empire and Europe for a start. I am quite sure there were Black guys who came on ships into the port and availed themselves of Monto ladies, but any sort of presence seems to be a case of serious conjecture and remarkable invisibility. Indeed if IRA fighters in the GPO did have a contingent of men from the colonies of any stripe that would surely have been noted and widely so as a wider part of the whole down with English colonialism, but again this seems to be a remarkably invisible contingent. A Canadian was noted, but that's where it seems to stop.

Yes there was a Black soldier, but even there he was an outlier. A few years back there was an episode of Doctor Who of all things that had British soldiers from Boer war times as part of the story and one of them was Black and a few people were calling revisionism on this. In the end they did some digging and did find one Black guy in a regiment from that time, but again he was an outlier.

And yet something pretty unusual; that is people from other British colonies helping the Irish cause has only been noted it seems in one book and not more widely? I could see how the British wouldn't be too keen on mentioning it alright, but it would have been a very nice propaganda piece for Irish Republicans that even non Irish people from other parts of the British empire were helping our just cause with a mind to their own. One could imagine them growing in the telling, yet nada. You've pointed out that there was some African American support which has been noted, but on the ground?

We know of others like the Polish born Herzog lad, the "Sinn Fein Rabbi" and fluent Irish speaker and Bob Briscoe who was one of the main armourers of the Republican forces and wider support from all sorts of quarters outside Ireland, but these other "forgotten dark skinned(students apparently)" GPO guys? Given it's one of the most picked apart narratives of our modern history and we're pretty damned sure of the names of the guys in that post office and many in the surrounding areas I'm really not buying this until anything approaching good evidence is to hand. Now I grant you that same narrative for many a year had everyone's grandfather in the GPO. So much so that if it were true the queue to get to O'Connell street would have stretched to Santry, but this smacks hard of a convenient revisionism. AKA in the parlance of Dublin a load of me bollex until proven otherwise.