Thalo Blue is Cyan1 of 4
CCCC, Grumbacher Thalo Blue, PB15.3, Transparent cyan.
Pathalocyanine Blue, a primary color in pigment, a secondary color in light.
Cyan in pigment as it gets darker receives more magenta and gradually takes on an ultramarine blue hue before becoming it's neutral dark shade in pigment by adding the opposite color red.
Like the polarizing Iceland Spar crystal which
It is permanent and synthetic.