For a proposition, such as:
P: Socrates is a man
Then not P is also a proposition:
Not P: Socrates is not a man
But do the same goes for properties? One can argue in the following way:
red is a property of red flags, or of red apples; but not red is not a property; for no thing instantiates not redness; that is not redness does not cohere in some substrate - here a flag, or apple; even though whiteness, which is an example of not redness, coheres in a white wall.
Q. Is this right?
All this, I think, takes it for granted that properties cohere in some substrate or substance - this is a commitment to a specific ontology; we may choose something else; the obvious choice being a world where all that there is are bundles of properties, and no substrate or substance to which to hang them on; there, existence is also a property - a property which all existing entities have.
Q. Given this ontological commitment; then is not P also a property?