EyeColorFilterType.php

                'apply_filter' => function (QueryInterface $filterQuery, $field, $values) {

                    if (empty($values['value'])) {
                        return null;
                    }

                    $paramName = sprintf('p_%s', str_replace('.', '_', $field));

                    // expression that represent the condition
                    $expression = $filterQuery->getExpr()->eq($field, ':' . $paramName);

                    // expression parameters
                    $parameters = array($paramName => $values['value']); // [ name => value ]
                    // or if you need to define the parameter's type
                    // $parameters = array($paramName => array($values['value'], \PDO::PARAM_STR)); // [ name => [value, type] ]

                    return $filterQuery->createCondition($expression, $parameters);
                },