somber vs drab

somber is not a noun while drab is a noun.

Word	Noun	Adjective	Verb	Adverb
somber	No	Yes	No	No
drab	Yes	Yes	No	No

As adjectives, somber and drab are synonyms defined as:

Other synonyms of somber include sober, sombre.

somber (noun)	drab (noun)
	a dull greyish to yellowish or light olive brown

somber (adjective)	drab (adjective)
lacking brightness or color; dull	of a light brownish green color
grave or even gloomy in character	lacking brightness or color; dull
	causing dejection
	lacking in liveliness or charm or surprise