Question: **The context:**

There is a population of people surviving on a lunar-analogue's surface, descended from the crew of a crashed spaceship. The rest of their society is not relevant to the question, but their technology includes cobbled together habitats and void suits that protect against some solar radiation but not all (an arbitrary amount that allows them to maintain a population, but not necessarily easily).

**The question:**

What skin colour would this select for? I'd initially say a pallid white given the lack of UV exposure, but I've recently stumbled upon research which suggest melanin provides at least some protection against gamma radiation: <https://www.news-medical.net/amp/news/20110824/Melanin-also-protects-from-ionizing-radiation.aspx>

The question is, what skintone would partial protection from gamma radiation on a longstanding permanent lunar culture select for?

For reference, this is for an art project where colour palette will be important, so injecting some realism into the skintone and working from there would be the way to go.

Answer: 
**Random.**

I am reminded of the teeth of the numbat.

[![numbat skulls](https://i.stack.imgur.com/Z0AOx.jpg)](https://i.stack.imgur.com/Z0AOx.jpg)
<http://animaldiversity.org/collections/contributors/anatomical_images/family_pages/dasyuromorphia/myrmecobiidae/>

The numbat has more teeth than any other land mammal. Tooth number and shape vary between individuals. It does not matter to the animal because none of the teeth are used at all. The numbat eats with its tongue exclusively.

> 
> The variability in number and form of teeth, as well as the lack of
>  significant tooth wear have been cited as. evidence that the teeth are
>  used very little and so are not subject to intense selection pressure
>  (Calaby 1960).
>  <https://www.environment.gov.au/system/files/pages/a117ced5-9a94-4586-afdb-1f333618e1e3/files/22-ind.pdf>
> 
> 
> 

So too skin color for your moon people. Skin color for earth humans is influenced by evolutionary pressures that have to do with UV damage / vitamin D synthesis. Absent selection pressures for or against given colors, skin color would evolutionarily drift, like the number and shape of teeth of the numbat. One could invoke this to explain why different individuals were colored differently one to the next: it is random. 

Note that it has taken the numbat millions of years for its teeth to reach this state. But with a small population you could have evolution / genetic drift happen faster.
Since skin colour affects appearance, sexual selection comes into play. Whatever skin colour their culture finds most attractive is what will be selected for.