Usually, gray teeth don't whiten as well as ones in the yellow shade range. Gray teeth may get lighter overall, but they will probably stay in the gray range and it may take longer to get there.
Does Bleaching Work on Gray Teeth?
Doctor Answers 2
Bleaching gray teeth
Traditionally, yellow stains do much better than gray teeth with today's whitening procedures. You will still see an improvement in the shading of your teeth- but you should adjust your expectation level accordingly. We have seen patients who started off with gray teeth walk out of our office with great results.