People who remember the old Napthalmide maroon, which was very popular in its day, might recognize this as a close approximation to that storied color.
The colour of night sky or shadows, very dark, reddish, semi-opaque blue with strong tinting, also known as Indanthrone. A versatile alternative to Ultramarine yet not as overpowering as Phthalo.
A transparent "quin," this single pigment color is a terrific start for brilliant reds and pinks as well as fiery glazes that are exactly what one associates with magenta.