What you say seems to depend on an over-simplified model of PageRank. But there is something in it that lines up with my experience. It is no longer true that any url gets the TBPR that it earns. Some types of pages (lists of links for example) seem to get flagged as an automaic gray bar - and that's that.

I used to think this was manual, and in the beginning it may have been. But now I think that original "seed set" has been used to generate a machine-learning algo that is intended to locate other pages of the same nature. This approach to various segmants of the algo is something that is more and more in use. All those PhD in Statistics folks need something to do, right?

For a while, my theoretical algorithm was misfiring quite a bit and the mysterious graybar disease was nearly epidemic. Just this past month, I'm seeing some of those peculiar gray bars come back to white or even green. That could indicate either that the machine-learning has improved, or something about its logic has been tweaked.

That's my story, and I'm sticking to it -- for now.

we have multiple pages that routinely alternate between PR3 / 4 and grey, and rank just the same whatever they're showing.

most of them are nothing at all like link exchange pages, so if thats what they're trying to do it's broken.

Google might have several reasons for the gray bar - but I can't quite focus in on what they all might be. Definitely, one reason was link selling.

One thing that puzzles me, is that I see pages with PR 1, that change to show Grey Bar a few days later, and back to PR 1 within weeks - totally unconnected with anyone calling a Toolbar PageRank update. It's like the Toolbar PR figure is varied by other factors on a very short timescale. I haven't watched PR for many many years, the observation initially came from a client who looked at it every week. I checked it out and confirmed it too.

Use this search to get a list of your pages that are gray barred.
-site:www.example.com/* site:www.example.com

Use this search to get a list of your pages that are not gray barred.
site:www.example.com/*
This list will correlate well (not perfectly due to delays) with Webmaster Tools "Links", "Pages with internal links".

"Supplemental" implies gray bar. There may be more reasons for gray barred pages, and more gray barred pages, if your site is in a serious penalty condition or banned altogether.

I believe one reason a page may be "gray barred" or "Supplemental" is the keywords for the page are simply not searched for very frequently.
Of course there are the many other standard causes, duplicate content, duplicate descriptions, perhaps excessive boilerplate interlinking, etc. ....

I dont believe that that search shows "the supplemental index".

some of our grey pages rank top 3 for competitive phrases and nearly all of them will show up for the first 3 or 4 words in their title.

and these are not unusual titles whatsoever.

From what I see the /* hack results have become a lot harder to understand or to count on - and since it was never a documented special search, there's no guarantee how Google handles it. I prefer looking at the results they export to their search partners, such as AOL. If a url isn't on those results, then I assume Google has placed it in something like the old supplemental index.

Some (even many) "Supplemental" pages do rank well these days. Google made a change a couple years back including pages that are supplemental and pages that are not supplemental in the SERPS. This of course brought up even more questions as to what the term "supplemental" meant; so Google simplified things removing the tag supplemental from the results pages. The concept still exists, only the test mentioned and the "gray barred" indications are clues to a page being in the "supplemental" state. I suspect the number of supplementals shown in the SERPS may be related to Google's server loading at the time of the query, and the decision for supplemental is partially based upon the page's keywords frequency of request by Google users.

Finally, today, one shouldn't make too aggressive a change to pages that are supplemental or gray barred, because the pages might be ranking just fine in the SERPS for their keywords. I have supplemental pages that rank well for their keyword terms and supplementals that I cannot find in the results pages without excessive effort!

how well would you expect to see one ranking then?

we have a page that on checking just now, is ranking #8 for "widget resources" on .co.uk out of 62,800,000 pages, (fairly competitive) where widget is a 3 letter keyword, 256,000,000 pages and just about as competitive as it gets.

surely nobody would think this page is in the supplementals because it's grey barred?

I have supplemental pages that rank number 1 for their terms. These are not rare keywords either. Years back when Google introduced "Supplemental", these pages would never show in the results, it was a killer.

Try tedster's suggestion, see if you can find your page in an AOL search? You may not be able to.

Some pertinent links:
[mattcutts.com...]

[mattcutts.com...]

"I think going forward, you’ll continue to see the supplemental results get even fresher, and website owners may see more traffic from their supplemental results pages."

When Google introduced the supplemental index they quickly realized some of the best "content" pages on the internet have NO PAGERANK AT ALL! With the introduction of "rel=nofollow" Google has really made pagerank meaningless. Now, everybody just hoards their pagerank (well mostly anyway).

>>Try tedster's suggestion, see if you can find your page in an AOL search? You may not be able to. <<

yep just looked, its in the same position on aol.co.uk out of 6,020,000 pages

Then you've got one of those "funny" graybars for that particular url - the kind whose reasons are often not obvious. But at least you're ranking and, I assume, getting traffic.

The other thing to remember is Tool Bar PR can lag actual PR and supplemental status by a large time period. Perhaps up to 3 months, so nothing ever matches exactly. There is simply a statistically significant correlation between the supplemental test and the gray toolbar.
I don't know how frequently Google updates AOL. For my sites, in most cases, pages that show up in the Google supplemental "test" are not in AOL's index. Again they do rank in Google searches, but are nowhere to be found in AOL searches.

Supplemental test.
-site:www.example.com/* site:www.example.com

I have seen this test stop functioning for periods of up to two weeks in the past.

I have tons of pages that go gray bar for a couple months, then pr6 for a few months then back to graybar.

Traffic never changes to them. These are unique highly linked pages that have been around for 9 years.

In my opinion whatever is causing this is more to do with looks then function and is probably geared to confuse webmasters. I mean really, out of the hundreds of direct friends I have and thousands of sub friends none have used the toolbar less webmasters/seo/sems.