What is the difference between blue and grey oyster mushrooms?

Blue and grey oysters are closely related cool-weather strains of Pleurotus ostreatus, and both are excellent for beginners. Blue oyster often shows a deeper blue-grey cap when young and fruits well in cooler conditions, while grey oyster is a touch more heat-tolerant and very productive. In practice they grow and taste very similarly, so either is a fine first strain.