There are very few situations in which you want to give users a full color pallet.
This is a tool that most advanced users don’t even need. I am seeing more and more full color pickers in web applications when allowing custom font colors, background colors, etc.
Users are not designers. They will not account for contrast, color relationships.
Instead, consider using a preset pallet that is designed to work with what you are theming. A great example of this is Youtube, which allows you to pick a duotoned theme for the embedded player chrome.