In sims2 it was always easy to switch between custom skintones when you were creating a sim, but as far as I know in sims 3 , you're only able to use 1 custom skintone

Is there a way to install several custom skintones, and that you can switch between them? Like when you would make 2 females, that you can choose a different skintone for both of them?

I'm not talking about the skincolor because I know you can shift that bar, I mean there are several custom skintones, shiny ones, more detailed ones, I just hate using the same skintone every time, and I don't get the chance to compare them when I can't switch between them

Not really, yet. Some experimenting is being done with doing them as accessories (like socks) but no way to actually add proper new skintones of yet.