Describes a deep, rich brown color. Used as a な-adjective or noun.
She has dark brown hair.
This leather sofa is dark brown and gives the room a calm atmosphere.
褐色 is brown in general; 濃褐色 adds the nuance of 'dark' or 'deep' brown.
Compound of 濃 (のう, 'dark, deep') + 褐色 (かっしょく, 'brown').