Adding support for editor color palette

gutenberg-color-palette.php

<?php

function prefix_setup_theme() {
	
	add_theme_support( 'editor-color-palette', array(
		array(
		    'name' => __( 'Strong Magenta', 'themeLangDomain' ),
		    'slug' => 'strong-magenta',
		    'color' => '#a156b4',
		),
		array(
		    'name' => __( 'Light Grayish Magenta', 'themeLangDomain' ),
		    'slug' => 'light-grayish-magenta',
		    'color' => '#d0a5db',
		),
		array(
		    'name' => __( 'Very Light Gray', 'themeLangDomain' ),
		    'slug' => 'very-light-gray',
		    'color' => '#eee',
		),
		array(
		    'name' => __( 'Very Dark Gray', 'themeLangDomain' ),
		    'slug' => 'very-dark-gray',
		    'color' => '#444',
		),
    ) );

}

add_action( 'after_setup_theme', 'prefix_setup_theme', 10 );