SolrQuery::addFilterQuery

<?php

$options = array
(
    'hostname' => SOLR_SERVER_HOSTNAME,
    'login'    => SOLR_SERVER_USERNAME,
    'password' => SOLR_SERVER_PASSWORD,
    'port'     => SOLR_SERVER_PORT,
);

$client = new SolrClient($options);

$query = new SolrQuery();

$query->setQuery($query);

$query->addFilterQuery('color:blue,green');

$query_response = $client->query($query);

$response = $query_response->getResponse();

print_r($response['facet_counts']['facet_fields']);

?>

The above example will output something similar to: