Guide to Open Access to Publications
Green Open Access means that a copy of a published article is archived in an open access repository, which can be either institutional or disciplinary or also managed by a research funder. The archived copy of the article is usually the Author Accepted Manuscript (i.e. the post-print); journals rarely permit the version of record (i.e. the publisher's version) to be archived. Some journals may also impose embargo periods before the copy of the article can be shared through a repository and repositories usually allow to indicate such embargo period when depositing the copy of the article. This way, the archived copy of the article can be deposited immediately upon publication and one does not need to wait for the embargo period to lapse before depositing.
Gold Open Access means that an article is published either in an open access journal or in a subscription-based journal that offers open access option for individual articles (the latter journals are described as hybrid journals). In hybrid journals and in many open access journals, the author or their institution is asked to pay article processing charges or open access fees either upon submission or upon publication.