From WordNet (r) 2.0 (August 2003) [wn]:
grayness
n : a neutral achromatic color midway between white and black
[syn: gray, grey, greyness]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Grayness \Gray"ness\, n.
The quality of being gray.
[1913 Webster]