Currently there is no UI to add music albums to collections nor to filter albums by collections in contrast to artists where this works well.
In my eyes it makes much more sense to organize albums by collections instead of artists. The current tagging capabilities for albums are quite minimalistic, only genres and sharing-labels. This does not allow to tag and filter albums in a meaningful way.
Please add a UI to collections for albums (and do not forget to update the mobile clients accordingly)!
BTW, the REST-API already supports collections for albums:
PUT http://localhost:32400/library/metadata/130001?collection.locked=1&collection[0].tag.tag=Test1&collection[1].tag.tag=Test2 GET http://localhost:32400/library/metadata/130001 <MediaContainer size="1" allowSync="1" identifier="com.plexapp.plugins.library" librarySectionID="28" librarySectionTitle="Hörbücher" librarySectionUUID="..." mediaTagPrefix="/system/bundle/media/flags/"mediaTagVersion="1434380690"> <Directory ratingKey="130001" key="/library/metadata/130001/children" parentRatingKey="130000" guid="com.plexapp.agents.none://130001?lang=xn" type="album" title="Per Anhalter ins All" parentKey="/library/metadata/130000" parentTitle="Adams, Douglas" summary="Nur noch wenige Minuten..." index="1" year="1996" thumb="/library/metadata/130001/thumb/1434031644"originallyAvailableAt="1996-01-01" leafCount="23" viewedLeafCount="0" addedAt="1335268049" updatedAt="1434031644"> <Genre id="9424" tag="Audio Book"/> <Collection id="24225" tag="Test1"/> <Collection id="24226" tag="Test2"/> <Field name="summary" locked="1"/> <Field name="collection" locked="1"/> </Directory> </MediaContainer>