The Collaborative International Dictionary of English v.0.48:

Greenness \Green"ness\, n. [AS. gr[=e]nnes. See Green.]
   1. The quality of being green; viridity; verdancy; as, the
      greenness of grass, or of a meadow.
      [1913 Webster]

   2. Freshness; vigor; newness.
      [1913 Webster]

   3. Immaturity; unripeness; as, the greenness of fruit;
      inexperience; as, the greenness of youth.
      [1913 Webster]

WordNet (r) 3.0 (2006):

greenness
    n 1: the lush appearance of flourishing vegetation [syn:
         greenness, verdancy, verdure]
    2: the state of not being ripe [ant: ripeness]
    3: green color or pigment; resembling the color of growing grass
       [syn: green, greenness, viridity]