No. As with many such myths, there is an element of truth in it. Many active mushrooms bruise blue. But not all of them do. Many boletes also bruise blue. Many blue bruising boletes are poisonous, causing gastrointestinal distress. There have also been poisonings due to people mistaking a darkening of a bruised mushroom with blueing. One young man in the San Francisco area was poisoned twice by Galerina species in this way (fortunately, he survived).