I recently changed my computer and reinstalled programs, including stud.io. In the screenshot you can see what went wrong: absolutely every part has no available colors. I only noticed this after installing biopack, khingkpack and galvapack, but maybe the problem appeared earlier.
Nope. The only “extra” palette that I found is in the list of palettes of parts and there it is possible to select a part of the initially defined color (not the fact that there are only available colors there).
Have you downloaded the color pack? A few months ago I tried to download it, and it made it so I couldn’t change the color of anything. (I should give it another go some time soon)