Could you use the query:
SELECT p.*, GROUP_CONCAT(StandardColor) AS AvailableColors FROM tbl_products AS p LEFT OUTER JOIN tbl_products ON tbl_products.RootModelNumber = p.RootModelNumber GROUP BY p.ProductID
and then use the search:
$searchrsDataSet_1->setSearch(array("type"=>"List", "comparison"=>"Includes", "join"=>"AND"), array("tbl_products.StandardColor"), "s", "color");