Sometimes you can see the logic behind a gray bar (pages of links with little other content, for example) but not in every case.
FWIW, I've seen otherwise good pages that aren't getting new links ... go to greybar. I get a link or two for them and the pages get the green again. It's happened too often to be a coincidence. (Note: The links have to be IBLs, internal linking doesn't kick start the return to green)