olive drab vs drab

olive drab and drab both are nouns.

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

As nouns, olive drab and drab are synonyms defined as:

olive drab (noun)	drab (noun)
a cloth of an olive-brown color used for military uniforms	a dull greyish to yellowish or light olive brown
military uniform of the United States Army; made from cloth of a dull olive color
a dull greyish to yellowish or light olive brown

olive drab (adjective)	drab (adjective)
	of a light brownish green color
	lacking brightness or color; dull
	causing dejection
	lacking in liveliness or charm or surprise