Just started playing around with this a bit. Still have no idea exactly what does what, why or how...
There's a lot to be gained by playing around with those settings though.
(No lights added, default render settings.)

Ah, the Natalie Dormer lookalike model!

First thing that comes to mind is Translucency. Maybe you're applying presents for the Translucency, that come with the product.
Open the Surface Tab, and choose one part of the skin (Torso for example), and see if the Translucency value and/or colour changes from one model to the other.

Yes, couldn't help myself with that one.

It's the same skin on all 3, just different surface-settings I found online (for skin) - I wanted to compare them, and use them as basepoints to learn some more about those settings. (still clueless though )

The answer lies in the skin Surface settings. You should tell use what settings you use, or better, share a print screen of said settings.
I'm not sure what you're asking here.

Oh.... I'm not asking anything, just making a statement about how much you can actually change without changing skins, and looking for other peoples experiences with it.

When I have some settings that I think makes a big difference, I'll share them - but for now, I'm just trying to figure out what the different settings does and what combinations works well.

Ah right.
Well, Translucency is one of those settings that make the skin reflect different hues of colour.