after_setup_theme

if ( ! function_exists( 'twentyfifteen_setup' ) ) :
/**
 * Sets up theme defaults and registers support for various GeChiUI features.
 *
 * Note that this function is hooked into the after_setup_theme hook, which
 * runs before the init hook. The init hook is too late for some features, such
 * as indicating support for post thumbnails.
 *
 * @since Twenty Fifteen 1.0
 */
function twentyfifteen_setup() {

	/*
	 * Make theme available for translation.
	 * Translations can be filed in the /languages/ directory.
	 * If you're building a theme based on twentyfifteen, use a find and replace
	 * to change 'twentyfifteen' to the name of your theme in all the template files
	 */
	load_theme_textdomain( 'twentyfifteen', get_template_directory() . '/languages' );

	// Add default posts and comments RSS feed links to head.
	add_theme_support( 'automatic-feed-links' );

	/*
	 * Let GeChiUI manage the document title.
	 * By adding theme support, we declare that this theme does not use a
	 * hard-coded  tag in the document head, and expect GeChiUI to
	 * provide it for us.
	 */
	add_theme_support( 'title-tag' );

	/*
	 * Enable support for Post Thumbnails on posts and pages.
	 *
	 * See: https://codex.gechiui.org/Function_Reference/add_theme_support#Post_Thumbnails
	 */
	add_theme_support( 'post-thumbnails' );
	set_post_thumbnail_size( 825, 510, true );

	// This theme uses gc_nav_menu() in two locations.
	register_nav_menus( array(
		'primary' => __( 'Primary Menu',      'twentyfifteen' ),
		'social'  => __( 'Social Links Menu', 'twentyfifteen' ),
	) );

	/*
	 * Switch default core markup for search form, comment form, and comments
	 * to output valid HTML5.
	 */
	add_theme_support( 'html5', array(
		'search-form', 'comment-form', 'comment-list', 'gallery', 'caption'
	) );

	/*
	 * Enable support for Post Formats.
	 *
	 * See: https://codex.gechiui.org/Post_Formats
	 */
	add_theme_support( 'post-formats', array(
		'aside', 'image', 'video', 'quote', 'link', 'gallery', 'status', 'audio', 'chat'
	) );

	$color_scheme  = twentyfifteen_get_color_scheme();
	$default_color = trim( $color_scheme[0], '#' );

	// Setup the GeChiUI core custom background feature.
	add_theme_support( 'custom-background', apply_filters( 'twentyfifteen_custom_background_args', array(
		'default-color'      => $default_color,
		'default-attachment' => 'fixed',
	) ) );

	/*
	 * This theme styles the visual editor to resemble the theme style,
	 * specifically font, colors, icons, and column width.
	 */
	add_editor_style( array( 'css/editor-style.css', 'genericons/genericons.css', twentyfifteen_fonts_url() ) );
}
endif; // twentyfifteen_setup
add_action( 'after_setup_theme', 'twentyfifteen_setup' );

/**
 * Overwrite block editor’s default color palette. 
 *
 * @return void
 */
function prefix_editor_color_palette() {
	add_theme_support( 'editor-color-palette', array(
		array(
		    'name'  => __( 'Storm Gray', 'themeLangDomain' ),
		    'slug'  => 'storm-gray',
		    'color' => '#6B6F82',
		),
		array(
		    'name'  => __( 'Martinique', 'themeLangDomain' ),
		    'slug'  => 'martinique',
		    'color' => '#2D2E4F',
		),
		array(
		    'name'  => __( 'Cornflower Blue', 'themeLangDomain' ),
		    'slug'  => 'cornflower-blue',
		    'color' => '#666EE8',
		),
		array(
		    'name'  => __( 'Radical Red', 'themeLangDomain' ),
		    'slug'  => 'radical-red',
		    'color' => '#FF4961',
		),
    ) );
}
add_action( 'after_setup_theme', 'prefix_editor_color_palette' );

<?php 
	
	add_action( 'after_setup_theme', 'gcdocs_i_am_a_function' );
	
	function gcdocs_i_am_a_function() {

		add_theme_support( 'title-tag' );
		add_theme_support( 'post-thumbnails' );
		add_theme_support( 'custom-header' );

	}

 ?>