@gertie47 I responded last evening then edited in some more skin editing details above, but I just realized that you appear to have the skin color options showing in your screenshot, so you must have this area open? Am I understanding correctly that the sim from the gallery does show the skin colors bye will not let you choose/edit it? Well, if this is the case you are correct, something is not working as it should. It's possible that something is buggy in the sim that you downloaded from the gallery, but it's also possible that something is wrong in your CAS skintone area already since you are seeing different options than I am, and I have all packs. Plus I was told that the red skintone option is from base game. So... you should be seeing the same skintone options that I do. Can you please try the following and see if the same editing options appear for you that I mentioned:
Close your game and move your Mods folder from your "The Sims 4" folder [Documents > Electronic Arts > The Sims 4] to your desktop (save it for reference) and delete the localthumbcache.package file in your “The Sims 4” folder. Then add this sim into a new game save and see if you see the red skin tone and other skin options and can then change her skin color. You can test without saving.