Gold Open Access refers to articles that are published in fully Open Access journals, where all the content is freely available to everyone without subscription fees or paywalls.
Since Open Access journals do not charge for access to content, they must operate on some other model to cover their costs. Some OA journals are funded by scholarly societies or professional organizations as part of their operations. Commonly, however, Gold OA means that authors pay to cover the costs of publication through publishing fees, often referred to as article processing charges, or APCs.
Those doing sponsored research may be able to include costs of publication in their funding proposals.
As an alternative to the "author pays" model, many libraries are entering into "read and publish" agreements, also called transformative agreements. In these cases, a single contract will cover subscription access to a publisher's journals for readers at an institution and APCs for Open Access articles published by authors affiliated with the institution. The CSU has an agreement like this with Elsevier, and may add agreements with more publishers.
Green Open Access means a version of an article, often the accepted version of the author's manuscript, is made available without charge, even if the published version is behind a subscription paywall. Most publishers have a Green OA or "self archiving" policy, which allows for sharing articles Open Access for greater exposure and to meet any funders' or institutional Open Access requirements.
You can check your publisher's site for their self archiving policy, or look up policies by journal title in Sherpa/Romeo, a database of Green OA policies.
If your publisher doesn't have a policy for Green OA, you may be able to negotiate permission for this as a part of your author agreement. The SPARC Author Addendum provides a document you can add to your author's agreement to retain your rights for self archiving.
Policies for Green OA or self archiving vary on many terms, such as...
What version of the article can be shared. The policy may allow sharing:
Where the article can be shared. Common options include:
When the article can be shared. Green OA policies sometimes require an embargo, or delay after publication, before the self archived version can be shared. Sometimes the length of the embargo will vary depending on the version being shared or the location where it is being shared.
You may hear other terms used to describe Open Access arrangements.