“Open access” (OA) simply means a paper is free to read online, with no subscription or paywall. But not all open access is the same — researchers use a set of color labels to describe how a paper became free. Knowing them helps you judge which version you're looking at and whether you can reuse it.
The colors of open access
- Gold — the paper is published open access on the journal's own site, usually because an APC was paid. It's the final, citable version and typically has a clear reuse license.
- Green — the journal is subscription-based, but a free copy (often the accepted manuscript) is legally archived in a repository like PMC or a university repository.
- Bronze — free to read on the publisher's site, but with no explicit open license. It can be made free temporarily and could disappear, so treat it as “free for now.”
- Diamond (or platinum) — open access with no fee to either readers or authors, usually run by a university, society, or non-profit. The fairest model, increasingly common.
What an APC is
An Article Processing Charge is the fee some open-access journals charge authors (or their funders/institutions) to publish, replacing subscription income. APCs range from modest to several thousand dollars. As a reader you never pay an APC — it only matters if you're the one publishing.
Licenses: what you're allowed to do
Truly open papers carry a Creative Commons license. CC BY lets you share and reuse the work (even commercially) as long as you credit the authors — the most permissive. CC BY-NC adds a non-commercial restriction, and CC BY-ND forbids derivatives. If a paper has no license, assume standard copyright: you can read it, but not redistribute it.
Which version am I reading?
- Preprint — the authors' draft shared before peer review. Fast and free, but not yet vetted; findings may change.
- Accepted manuscript (AAM) — the peer-reviewed text, before the publisher's final formatting. Scientifically identical to the final paper.
- Version of Record (VoR) — the publisher's final, typeset, citable version. The one to cite when you can.
Rule of thumb: cite the Version of Record when you have access to it; a preprint or accepted manuscript is fine to read and learn from, but note which version you used.
A word on predatory journals
Some low-quality journals exploit the APC model — they take a fee and publish almost anything with little or no real peer review. Warning signs include aggressive spam invitations, promises of impossibly fast publication, fake or hidden editorial boards, and no indexing in trusted databases. A quick check: is the journal listed in the Directory of Open Access Journals (DOAJ)? Legitimate OA journals usually are.
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