wp ajax

var data = {
       action: 'image_color',
       id: 1234
   }

//jQuery
jQuery.ajax(
   {
   url: " http://domain.com/wp-admin/admin-ajax.php",
   type: "POST",
   data: data,
   success: function (result) {
           alert('success');

   }
});   



//in function.php
add_action( 'wp_ajax_function_name', 'function_name' );
add_action( 'wp_ajax_nopriv_function_name', 'function_name' );

function function_name() {
 echo "string";
}