the crowned pigeons are easy if you remember a couple of rules, and there are only three species.
One: if it has a white-tipped crest it is a Victoria crowned pigeon.
Two: if the crest has no white tips, then look at the breast. Blue crowned pigeon (aka western or common) has a blue breast, while maroon-breasted (aka Sclater's/Scheepmaker's or southern) has a maroon breast (or red or whatever you want to call the colour).
(There are two subspecies of maroon-breasted crowned pigeon but the only one you'll see is sclateri because that's the only one in Europe).
So, Victoria has a white crown (like the Queen); blue has a blue breast; maroon-breasted has a maroon breast but no white crown.