There are different types of Open Access (OA) publications:
Gold OA refers to publications in an open access journal (for example PLOS journals) for which the Article Processing Cost (APC) has been payed by authors, institutes, or research funders.
Green OA refers to publications in a journal that are also available in an open access repository. These publications
(pre-prints or post-prints with publisher permission) are whether self-archived in either an institutional or disciplinary repository (such as arXiv.org) by the authors/librarians or archived in systems such as PubMed Central (PMC).
Bronze OA refers to publications in a journal that are open access and free to read on publisher’s website (but not free to reuse, adapt, or share) after the embargo period. These publications are not considered as real open access since there is no clear license/terms of (re)use that can be revoked at any time by the publisher.
Hybrid OA (payed OA) refers to publications in a subscription journal that are open access. Hybrid journals offer authors (for a fee) the option of making their articles open access. These journals have both closed and OA articles.
For more information on OA colors visit:
https://en.wikipedia.org/wiki/Open_access
Also, as explained here, Unpaywall offers the different colors of Open Access if it is enabled in the plugin. How does Unpaywall define green, gold, bronze, and hybrid types of OA is shown bellow:
Is article OA?
Visit this page: How to determine Open Access (OA); Tools to determine Open Access (OA) Publications