i have 3 arrays, i want to get the result of those 3 arrays in one, but how can i deleted those same answer in a arrays?

here's my example:

<?php
$array1 = array("a" => "green", "red", "blue");
$array2 = array("b" => "green", "yellow", "red");
$array3 = array("c" => "white", "blue", "black");
$result = ??? ($array1, $array2, $array3);
print_r($result);
?>

Array
(
    [0] => green
    [1] => red
    [2] => blue
    [3] => yellow
    [4] => red
    [5] => white
    [5] => black
)

please help me guys.. thank you..