It's blue, it's schist, it's Blueschist!

Blueschist really IS blue, at least at it's Greek type-section at Ambelakia south of Mt Olympos.
The blue color is, one supposes, due to the presence of glaucophane, a blue amphibole. Mostly what is apparent in the rock is micaceous. This makes it look more phyllitic than schist-istic, but possibly this is merely an alteration affect. Could be retrograde metamorphism, but let's keep things simple.

This little rock baby looked quite dull until scanning shows it lovely -- no Bob, I didn't change the colors.