burnt umber vs umber

burnt umber and umber both are nouns.

Word	Noun	Adjective	Verb	Adverb
burnt umber	Yes	No	No	No
umber	Yes	Yes	No	No

As nouns, burnt umber and umber are synonyms defined as:

Other synonyms of burnt umber include chocolate, coffee, deep brown.

As nouns, umber is a hypernym of burnt umber; that is, umber is a word with a broader meaning than burnt umber:

burnt umber (noun)	umber (noun)
a medium brown to dark-brown color	a medium brown to dark-brown color
dark brown pigment obtained by heating umber	an earth pigment

burnt umber (adjective)	umber (adjective)
	of the color of any of various natural brown earth pigments