This is the link you're looking for: https://www.colodore.com/
If you're interested in how this palette (editor) was derived, read this: https://www.pepto.de/projects/colorvic/.
The discussion on the above site is an update of the original post by the same author: https://www.pepto.de/projects/colorvic/2001/
Interesting. I have the pixel art book Pepto refers to, it is very nice.
On my screen that doesn't match videos of actual C64's on actual CRT's. (It also doesn't match my memory of them, but that's a whole lot less reliable)