cobalt ultramarine vs cobalt blue

cobalt ultramarine and cobalt blue both are nouns.

Word	Noun	Adjective	Verb	Adverb
cobalt ultramarine	Yes	No	No	No
cobalt blue	Yes	No	No	No

As nouns, cobalt ultramarine and cobalt blue are synonyms defined as:

cobalt ultramarine and cobalt blue: greenish-blue pigment consisting essentially of cobalt oxide and alumina

cobalt ultramarine (noun)	cobalt blue (noun)
greenish-blue pigment consisting essentially of cobalt oxide and alumina	a shade of blue tinged with green
	greenish-blue pigment consisting essentially of cobalt oxide and alumina