Source : Webster's Revised Unabridged Dictionary (1913)

Blackness \Black"ness\, n.
   The quality or state of being black; black color;
   atrociousness or enormity in wickedness.

         They're darker now than blackness.       --Donne.

Source : WordNet®

blackness
     n 1: the quality or state of the achromatic color of least
          lightness (bearing the least resemblance to white) [syn:
           {black}] [ant: {white}]
     2: total absence of light; "they fumbled around in total
        darkness"; "in the black of night" [syn: {total darkness},
         {lightlessness}, {pitch blackness}, {black}]