Gutenberg provides a default color palette to work with, but any theme can override this and provide their own.

• There are no limits on the amount of colors you can add to your palette
• Colors will be displayed in the order they are declared in your code
• 3-digit shorthand is allowed

add_theme_support( 'editor-color-palette',
	'#a156b4',
	'#d0a5db',
	'#eee',
	'#444'
);

Add this code to the functions.php file of your theme.

NOTE: Regardless of the colors you choose, you'll probably want to make sure you include both black (#000) and white (#fff).

Disable Custom Color Wheel

You'll notice in the image above, there is no custom color wheel. That's because I have disabled that as well.

We've published another article on how to disable custom colors here.

Brian Gardner has also written a nice article on this topic, and extended it to work with Genesis theme colors in the Customizer.