You could, by a similar method, generate all possible images but that doesn't mean you would be able to copyright them all. The creative element would become the act of identifying specific images within your set with artistic merit -- those would be copyrightable.

Nope, there is no "merit test" for copyright. Copyright attaches when the creation is fixed in tangible form.

You're right. Sorry, merit is a loaded term in copyright discussions. I don't mean that they would have to argue that their choice of images has artistic merit, but that the artist would probably think it does to pick it out of the billions.

It's not a "merit test", it's just "these are the ones the artist chose".

Copyright attaches to creative works when they are fixed in tangible form. An exhaustive list of every combination of colors in order is not creative.

That list wouldn't be copyrightable, since it contains no creative elements.