Description:
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Consider:

$safeColors = array(1,2,3,4,5,6,7,8,9,0,'a','b','c','d','e','f');
var_dump(in_array('T', $safeColors));

People not paying attention would assume "false", however, because T is compared 
with integers, it seems to be cast to 0, therefore, outputting true.

A "solution" would be a warning on the in_array page, as this isn't a problem with 
the function, just something that confuses users who aren't expecting it.