$a1=array("a"=>"red","b"=>"green","c"=>"blue","d"=>"yellow");
$a2=array("e"=>"red","f"=>"black","g"=>"purple");
$a3=array("a"=>"red1","b"=>"red","h"=>"yellow");

$result=array_intersect($a1,$a2,$a3);

// Output
// Array ( [a] => red )