Regarding the Custom Colors. I think it would be more user friendly if the user could make their own palettes simply by pasting in some hex like:
#0468BF #22A2F2 #52B5F2 #5BC6F5 #91E0F2
Adobe color picker makes is so easy to find palettes and then we could use them instead of only have the choices of the author.
https://color.adobe.com/search?q=ocean%20blue