From WordNet (r) 2.0 (August 2003) [wn]:
greyness
n : a neutral achromatic color midway between white and black
[syn: gray, grayness, grey]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
greyness \greyness\ n.
a neutral achromatic color midway between while and black.
Syn: gray, grayness, grey.
[WordNet 1.5]