ceruleum

from The Century Dictionary.

• noun A blue pigment, consisting of stannate of protoxid of cobalt, mixed with stannic acid and sulphate of lime. Ure, Dict. Also spelled cæruleum.

from the GNU version of the Collaborative International Dictionary of English.

• noun A greenish blue pigment prepared in various ways, consisting essentially of cobalt stannate. Unlike other cobalt blues, it does not change color by gaslight.