Green open access is through repositories separate from journal publishers. Journal publishers may embargo an author's work for a period of time before the author is able to make their work accessible through a repository, usually in manuscript format.
Gold open access is through open access journals, where articles are freely accessibly immediately upon publication.
A hybrid open access journal is one that charges a subscription/access fee, but also gives authors the option to publish individual articles as open access. Readers then get free access to some but not all content, and publishers collect revenue from author-side fees and reader-side subscriptions.