brown vs spectral colour

brown and spectral colour both are nouns.

Word	Noun	Adjective	Verb	Adverb
brown	Yes	Yes	Yes	No
spectral colour	Yes	No	No	No

As nouns, spectral colour is a hypernym of brown; that is, spectral colour is a word with a broader meaning than brown:

Other hypernyms of brown include chromatic color, chromatic colour, spectral color.

brown (noun)	spectral colour (noun)
an orange of low brightness and saturation	a color that has hue

brown (adjective)	spectral colour (adjective)
(of skin) deeply suntanned
of a color similar to that of wood or earth

brown (verb)	spectral colour (verb)
fry in a pan until it changes color
make brown in color