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]

Moby Thesaurus II by Grady Ward, 1.0:

127 Moby Thesaurus words for "greenness":
   acerbity, acescency, acidity, acidulousness, adolescence,
   agnosticism, amateurishness, amateurism, blankmindedness,
   brand-newness, callowness, coarseness, crudeness, crudity,
   cullibility, deceivability, dewiness, dryness, dupability,
   easiness, empty-headedness, freshness, gloss of novelty,
   greenhornism, gullibility, hiatus of learning, hoaxability,
   hyperacidity, ignorance, ignorantism, ignorantness, immatureness,
   immaturity, inanity, inexperience, infancy, ingenuousness,
   innocence, intactness, juiciness, juniority, juvenility,
   know-nothingism, knowledge-gap, lack of information, lateness,
   maidenhood, minority, mint condition, naiveness, naivete, naivety,
   nescience, newbornness, newfangledness, newfangleness, newness,
   nonage, nondevelopment, novelness, novelty, nowness, obscurantism,
   originality, oversimplicity, oversimplification, persuadability,
   presentness, pristineness, puberty, pubescence, pungency, rawness,
   recency, recentness, reductionism, roughness, rudeness, sappiness,
   seduceability, simpleness, simplicity, simplism, softness, sour,
   sourishness, sourness, spring, springtide, springtime, strangeness,
   subacidity, tabula rasa, tartishness, tartness, the rough,
   unaccustomedness, unacquaintance, unacquaintedness, uncommonness,
   uncultivation, undevelopment, unexperiencedness, unfamiliarity,
   unfinish, unfinishedness, unfledgedness, unintelligence, unknowing,
   unknowingness, unpracticedness, unprofessionalism,
   unprofessionalness, unrefinement, unripeness, unsophistication,
   unsweetness, unusualness, vacuity, vacuousness, verjuice,
   vinegariness, vinegarishness, virginity, weakness, youthfulness,
   youthhood