There are a control and 4 tests, but the results for the listed browsers there have only 3 letters, like GGR. Shouldn't there be five for each browser? Otherwise, which three of the five are you testing?
It is my understanding that the correct sequence is GGBG. I believe that if < 4 are given for a browser, then it is the first few that are tested; assume black if it isn't listed. This abbreviation is because later tests cannot be expected to work if earlier ones don't, so it's not worth listing them (though it's still a little inconsistent which are listed).
Because the page is so old (even before Aaron died), the only one of the browsers mentioned that I can verify is
IE6/Win: GBBB
I believe that 3 is guaranteed to be black if either 1 or 2 are black (making the IE5/Mac and Safari results slightly redundant). I believe that 4 is guaranteed to be black if 2 is black or 3 is red, meaning that it's not worth showing for any of them (... except for Opera 7b2 after refresh. Dang, I thought I had it figured out).