Source

File: wp-includes/theme.php

function display_header_text() {
	if ( ! current_theme_supports( 'custom-header', 'header-text' ) ) {
		return false;
	}

	$text_color = get_theme_mod( 'header_textcolor', get_theme_support( 'custom-header', 'default-text-color' ) );
	return 'blank' !== $text_color;
}