Golden Path (Open Access First Publications)
In this model, the publication appears in the form of a first publication directly in open access, usually with a publisher. In most cases, publication fees (article processing charges = APC) are charged for this.
Green Way (Second Publication, Self Archiving)
In this model, restricted scientific publications are published on non-commercial repositories either in parallel with the first publication or a second time after it, and are now made available to readers in open access. Many publishers now allow secondary publication, usually under certain conditions, such as compliance with an embargo period.
In this model, publication takes place in a so-called "hybrid journal". This is subscription-based and thus not accessible free of charge. However, authors have the option of having their article published in open access for a fee. This can be done either directly upon publication or at a later date. The model is thus a subform of the Golden Road.
Open Access without Open Content License (Free to Read)
In this model, the publication is available to the reader free of charge via the publisher's site or via a repository. However, the publication is not published under an open content license. The respective copyright and right of use or exploitation therefore apply.