First of all, before I say anything else, I'd like to thank two people for making these possible!
To JasonDuskey, who created a great tutorial on how to do this. Unfortunately, I cannot find it anymore. When I do, I will update this post!
To BobcatBen, who created the Global Skin Preserver
that made it even possible to keep your skins from reverting back to the original. Go to the Download page, and grab the file called Global Skin Preserver.
(you will need to download his file for these to work)
These vials are enabled for Children through Elder (I've never seen them enabled for children, and they kind of float in the air when they change, but it does work just fine!)
These are found in Buy Mode / Hobbies / Miscellaneous
They cost $150 each
Simple instructions: "Drink" changes to the new skin & "Antidote" changes them back
Sims will keep their new skin when they age
But babies and toddlers can't use them, and your genetics won't change.
Here are the links for the skintones:
Terminator / Terminatrix
Miradorn - This is a full sim
Bynar - This is a full sim
Tarchannen III Alien
I hope you have fun with these!