gutenberg-colour-scheme.php

<?php

function cameronjonesweb_colour_scheme() {
	return array(
		array(
			'name'  => 'White',
			'slug'  => 'white',
			'color' => '#ffffff',
		),
		array(
			'name'  => 'Black',
			'slug'  => 'black',
			'color' => '#222222',
		),
	  	array(
			'name'  => 'Grey',
			'slug'  => 'grey',
			'color' => '#f4f4f4',
		),
	);
}

/**
 * Generate CSS rules for the colour scheme
 *
 * @return string
 */
function cameronjonesweb_generate_colour_scheme_styles() {
	$colours = cameronjonesweb_colour_scheme();
	$styles  = '';
	if ( ! empty( $colours ) ) {
		foreach ( $colours as $colour ) {
			$styles .= sprintf(
				'.has-%1$s-color { color: %2$s; } .has-%1$s-background-color { background-color: %2$s; }',
				$colour['slug'],
				$colour['color']
			);
		}
	}
	return $styles;
}

/**
 * Render style tag with the colour scheme styles
 */
function cameronjonesweb_render_colour_scheme_styles() {
	wp_add_inline_style( 'wp-block-library', cameronjonesweb_generate_colour_scheme_styles();
}

add_action( 'init', 'cameronjonesweb_render_colour_scheme_styles' );