Build an array with CSS classes and inline styles defining the colors
which will be applied to the navigation markup in the front-end.

function block_core_navigation_submenu_build_css_colors( $context, $attributes ) {
	$colors = array(
		'css_classes'   => array(),
		'inline_styles' => '',
	);

	$is_sub_menu = isset( $attributes['isTopLevelItem'] ) ? ( ! $attributes['isTopLevelItem'] ) : false;

	// Text color.
	$named_text_color  = null;
	$custom_text_color = null;

	if ( $is_sub_menu && array_key_exists( 'customOverlayTextColor', $context ) ) {
		$custom_text_color = $context['customOverlayTextColor'];
	} elseif ( $is_sub_menu && array_key_exists( 'overlayTextColor', $context ) ) {
		$named_text_color = $context['overlayTextColor'];
	} elseif ( array_key_exists( 'customTextColor', $context ) ) {
		$custom_text_color = $context['customTextColor'];
	} elseif ( array_key_exists( 'textColor', $context ) ) {
		$named_text_color = $context['textColor'];
	} elseif ( isset( $context['style']['color']['text'] ) ) {
		$custom_text_color = $context['style']['color']['text'];
	}

	// If has text color.
	if ( ! is_null( $named_text_color ) ) {
		// Add the color class.
		array_push( $colors['css_classes'], 'has-text-color', sprintf( 'has-%s-color', $named_text_color ) );
	} elseif ( ! is_null( $custom_text_color ) ) {
		// Add the custom color inline style.
		$colors['css_classes'][]  = 'has-text-color';
		$colors['inline_styles'] .= sprintf( 'color: %s;', $custom_text_color );
	}

	// Background color.
	$named_background_color  = null;
	$custom_background_color = null;

	if ( $is_sub_menu && array_key_exists( 'customOverlayBackgroundColor', $context ) ) {
		$custom_background_color = $context['customOverlayBackgroundColor'];
	} elseif ( $is_sub_menu && array_key_exists( 'overlayBackgroundColor', $context ) ) {
		$named_background_color = $context['overlayBackgroundColor'];
	} elseif ( array_key_exists( 'customBackgroundColor', $context ) ) {
		$custom_background_color = $context['customBackgroundColor'];
	} elseif ( array_key_exists( 'backgroundColor', $context ) ) {
		$named_background_color = $context['backgroundColor'];
	} elseif ( isset( $context['style']['color']['background'] ) ) {
		$custom_background_color = $context['style']['color']['background'];
	}

	// If has background color.
	if ( ! is_null( $named_background_color ) ) {
		// Add the background-color class.
		array_push( $colors['css_classes'], 'has-background', sprintf( 'has-%s-background-color', $named_background_color ) );
	} elseif ( ! is_null( $custom_background_color ) ) {
		// Add the custom background-color inline style.
		$colors['css_classes'][]  = 'has-background';
		$colors['inline_styles'] .= sprintf( 'background-color: %s;', $custom_background_color );
	}

	return $colors;
}