amber vs yellow-brown

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

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

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

Other synonyms of amber include brownish-yellow.

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

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