This idiom ‘être fleur bleue’ literally translates as ‘to be a blue flower’, but is used in the context of describing someone as being ‘naively sentimental’.
This idiom originated from the novel ‘Heinrich Von Ofterdingen’ by the philosopher Georg Philipp Friedrich Freiherr von Hardenberg, known as Novalis, about a wandering minstrel who finds a blue flower, the symbol of poetry.
In the language of flowers, pale blue flowers are seen to be tender and innocent, with a vulnerability that compares to someone who is naive and sentimental. Such symbolism of the colour of pale blue has been used in contexts such as Mary, mother of Jesus, who is depicted as wearing pale blue garments which emphasise her purity of body and soul.
Adelbert von Chamisso, a German poet and botanist, believed Novalis’ depiction of the blue flower to be the core of Romanticism, Novalis communicating that personal inward cognition is possible only through thinking, feeling and contemplation, which can be traced back to Heinrich von Ofterdingen’s fascination with a naively sentimental blue flower.
Sources:
un secret de polichinelle 