@Chlidonias Why do they switch the Western and Sclater's images between diagrams? I assume you are taking the first diagram as the definitive one, so I guess that figures although from what I've seen sources online are really quite hazy on the morphological differences between Sclater's and Scheepmaker's. Thanks for the ID though, very helpful .
@amur leopard I never noticed they had swapped the two between the diagrams! But yes, the first one is correct. The species are easy to tell apart - victoria is the only one with white in the crest (like a queen's crown - all the others have plain blue crests); cristata has all blue underparts with the maroon colour only on the back and wings (hence Blue Crowned Pigeon); sclaterii has maroon underparts and wing; scheepmakeri has maroon underparts and a blue wing. Confusion only comes because sclaterii was formerly a subspecies of scheepmakeri, so websites will often give you descriptions for the former under the name of the latter. There can also sometimes be the added problem of hybrids in captive birds (e.g. between cristata and sclateri).