Override Block Editor Palette Colors

add_filter( 'wp_theme_json_data_theme', function ( $theme_json ) {

	$new_data = array(

		'settings' => array(

			'color' => array(

				'palette' => array(

					// Replace with your desired colors.

					array(

						'slug'  => 'white',

						'color' => '#ffffff',

						'name'  => 'White',

					),

					array(

						'slug'  => 'black',

						'color' => '#000000',

						'name'  => 'Black',

					),

					array(

						'slug'  => 'red',

						'color' => '#ff0000',

						'name'  => 'Red',

					),

					array(

						'slug'  => 'green',

						'color' => '#00ff00',

						'name'  => 'Green',

					),

					array(

						'slug'  => 'blue',

						'color' => '#0000ff',

						'name'  => 'Blue',

					),

				),

			),

		),

	);

	return $theme_json->update_with( $new_data );

} );