RoMEO has used different colours to help highlight publisher’s archiving policies. These colours are a development from the original RoMEO project list, and differentiate between four categories of archiving rights:

Each publisher's entry is coded according to one of these colour categories.

The entry for each publisher also lists conditions or restrictions imposed by the publisher which govern archiving rights or activities.

Conditions are taken as terms which can be easily accommodated and which do not hinder an author in archiving their work. A typical condition is to acknowledge the publisher's copyright in the work. Restrictions are more prohibitive, typically requiring some additional action on behalf of the author. Where a Restriction effectively blocks access to the eprint, such as in the case of an embargo on its public release, or requiring password-controlled access, then the partial archiving right is noted but the full colour categorisation does not apply.

Sometimes open access discussions talk about "gold" publishers. This is a later development independent of RoMEO categories, and is used to describe publishers of open access journals. For the purposes of archiving, all open access journals allow archiving and can be taken as RoMEO "green".

Some of the larger publishers have different archiving rights for different journals. This is particularly the case where they publish learned society journals on behalf of the society. A learned society might insist on a more liberal, or more restrictive archiving policy than the general publisher's copyright agreement allows. The RoMEO colour coding relates to the overall permissions given by a publisher. For example, a publisher has to apply the "green" archiving rights across all of their journals for their code to be "green".

Source: RoMEO Colours