No.004 in the Plantlife Series are all blue hues.
Top left: Even I know this one Cornflower! Yay. Centaurea cyanus (Cornflower, Bachelors button, Bluebottle, Boutonniere flower, Hurtsickle, Cyani flower) Wikipedia
Lower left: Nigella damascena (love-in-a-mist, ragged lady) again thanks Wikepidia
Lower Right: I can't pin this one down, although I think it could be some kind of Geranium Blue, however I could be way off with that. Please, I welcome being corrected. :-)
and Top Right, I have no idea! After much scanning of many websites and even using reverse google image search no luck.
Have a great day. LTS. :-D