[@Excal] No problem, it allows me to test the limits of all that I've considered and what I should consider. 

As for births in general, children are often born in a Custodia run clinic/hospital, and administered an I.T. there. Those who are detected to not have an I.T. and are without accountable guardians, are taken by the Magistratum afterwards and inducted into their combat academies. They do these 'recruitment drives' pretty frequently. Those who are born from the outside, though such cases are very specific and rare, are scanned for any dangerous genetic flaws before allowed into the walls. If they are deemed too tainted by the Apothos System, they are 'disposed' of. Certain physical mutations do not play into the success or failure of this scan, as it seems. Being that there are plenty of people in the Slums with slight mutations. Black hair is seen as a common harmless mutation, and naturally darker skin complexions. As there is no actual sunlight to speak of, the 'evolutionary' need for such things has since dwindled and have shown significant decline. 

But of course, I don't want to get too science-y. Kinda ruins the fun of the 'fantasy' bits. 'Rule of Cool', as I like to tout.