/*
结果如下：

array
(
    [0] => array
        (
            [0] => blue
            [2] => yellow
        )

    [1] => array
        (
            [0] => black
            [2] => green
        )

)

array_diff语法

array array_diff ( array $array1 , array $array2 [, array $ ... ] )
对比较array1和array2返回差异。
*/
$array1 = array("a" => "green", "php100.com", "blue", "red");
$array2 = array("b" => "green", "yellow", "red");
$result = array_diff($array1, $array2);

print_r($result);

/*
array
(
    [1] => blue
)