yellow-brown vs amber

yellow-brown is not a noun while amber is a noun.

Word	Noun	Adjective	Verb	Adverb
yellow-brown	No	Yes	No	No
amber	Yes	Yes	No	No

As adjectives, yellow-brown and amber are synonyms defined as:

Other synonyms of yellow-brown include brownish-yellow.

yellow-brown (noun)	amber (noun)
	a deep yellow color
	a hard yellowish to brownish translucent fossil resin; used for jewelry

yellow-brown (adjective)	amber (adjective)
of a medium to dark brownish yellow color	of a medium to dark brownish yellow color