According to Harnad et al, self-archiving works. Open access articles
are cited from 2.5 to 5 times as much as subscription-restricted
articles, according to their study. The “green” refers to a
publisher’s “green light” for the author to self-archive a paper in
some form, which may at least be available to some researchers, if not
the “gold,” which is open access from the time of publication.
(Source; Georgia State Libraries Issues in Scholarly Communication)