cobalt blue vs cobalt ultramarine

cobalt blue and cobalt ultramarine both are nouns.

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

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

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

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