ize_hex_color() when possible.
 *
 * Saving hex colors without a hash puts the burden of adding the hash on the
 * UI, which makes it difficult to use or upgrade to other color types such as
 * rgba, hsl, rgb, and HTML color names.
 *
 * Returns either '', a 3 or 6 digit hex color (without a #), or null.
 *
 * @since 3.4.0
 *
 * @param string $color The color value to sanitize. Can be with or without a #.
 * @return string|null The sanitized hex color without the hash prefix,
 *                     empty string if input is empty, or null if invalid.
 */
function sanitize_hex_color_no_hash( $color ) {
	$color = ltrim( $color, '#' );

	if ( '' === $color ) {
		return '';
	}

	return sanitize_hex_color( '#' . $color ) ? $color : null;
}

/**
 * Ensures that any hex color is properly hashed.
 * Otherwise, returns value untouched.
 *
 * This method should only be necessary if using sanitize_hex_color_no_hash().
 *
 * @since 3.4.0
 *
 * @param string $color The color value to add the hash prefix to. Can be with or without a #.
 * @return string The color with the hash prefix if it's a valid hex color,
 *                otherwise the original value.
 */
function maybe_hash_hex_color( $color ) {
	$unhashed = sanitize_hex_color_no_hash( $color );
	if ( $unhashed ) {
		return '#' . $unhashed;
	}

	return $color;
}