the quality or state of being black.
the quality or state of being a black person.

Origin of blackness

Middle English word dating back to 1300–50; see origin at black, -ness Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for blackness

Word Origin and History for blackness

late 14c., from black (adj.) + -ness.

Online Etymology Dictionary, © 2010 Douglas Harper