magento_soap_catalog_product_create_attribute_options.php

<?php
$options = $proxy->call($sessionId, 'catalog_product_attribute.options', array('23'));
foreach ($options as $opt) {
	if ($opt['label'] == 'yellow') {
		$color = $opt['value'];
	}
}
if (!isset($color)) {
	$color = $proxy->call($sessionId, 'catalog_product_attribute.addOption', array('23','yellow'));
}

$options = $proxy->call($sessionId, 'catalog_product_attribute.options', array('24'));
foreach ($options as $opt) {
	if ($opt['label'] == 'XL') {
		$size = $opt['value'];
	}
}
if (!isset($size)) {
	$size = $proxy->call($sessionId, 'catalog_product_attribute.addOption', array('24','XL'));
}