In a problem asking for a point as an answer in Context('point'), having both
$showPartialCorrectAnswers = 0;
install_problem_grader(~~&std_problem_grader);
is not sufficient to suppress messages such as
The second coordinate is incorrect
In this case, as discussed on
http://webwork.maa.org/pod/pg_TRUNK/doc/MathObjects/MathObjectsAnswerCheckers.html#flags_for_point____cmp
it is sufficient to use
ANS( $pt -> cmp( showCoordinateHints => 0 ) );
in order to not reveal info about a (partially) incorrect answer.
I suspect the answer coloring situation is different, but I did write "off-chance" ;-)