Someone once said,
“There are brave mushroom eaters and there are old mushroom eaters, but there are not old, brave mushroom eaters.”
Certainly Amanita and most other forms of toxic mushrooms turn a very characteristic blue upon a fresh break of the top-cap flesh. Absolutely preventable. But a poor little girl had her life destroyed.
A fair number of prime edible mushrooms, such as the boletes, also turn blue when the flesh is bruised.
In fact most Amanitas do not turn blue when bruised. Looking in the Audubon Society Field Guide to North American Mushrooms neither Amanita phalloides (Death Cap) or the next most lethal mushroom in the world, Amanita virosa (Destroying Angel) turn blue.
Be careful out there.