Blue is one of the last colours to be recognised and named in most cultures. Black and white are the first, followed by red. Blue, despite it being the sometime colour of the sky and sea, comes rather late.
I learnt this and more from New York's Radiolab, broadcast via Sydney's ABC Radio National Science Show, on my phone in London. The segment started with Homer's rather odd use of colour in the Iliad and Odyssey and the absence of the word blue in either publication, and ended with an intriguing experiment by a scientist on his child, discovering that it wasn't immediately obvious that the sky was indeed blue. All very interesting.
The day before I had watched Dr James Fox explicate the origins of the colour blue in art in the second instalment of his series A History of Art in Three Colours. Somewhere near the middle of the show he plucked a blue iris from the Alps of Europe. This flower was used to illustrate the importance of the colour blue in a famous unfinished novel, Heinrich von Ofterdingen, written in the late eighteenth century by Friedrich von Hardenberg (under the pseudonym of Novalis). Heinrich, a young boy, has visions that keep him from sleep. It turns out he longs not for treasures but for a blue flower, and the blue flower becomes a symbol of the German romantic movement.
It's not clear what von Hardenberg's blue flower was. I've seen a sweet pea mentioned on the web and Dr Fox seemed happy enough with an iris. Although blue is a relatively uncommon flower colour, I noticed a Purple Gromwell (Lithophora diffusa) from southern Europe out in flower today with what I would have described as blue flowers.
Here in the UK, the longing now is more for blue skies than blue flowers, but this slightly tatty flower of Gentiana angustifolia seems a reasonable substitute. It may well be close to what von Hardenberg had in mind. Gentians grow naturally in the mountains of Europe and the flowers of most species have an intensely blue colour.
The Merriam-Webster Dictionary describes Gentian Blue as 'a moderate purplish blue that is redder, lighter, and stronger than marine blue, bluer and duller than average cornflower, and bluer and lighter than old glory blue'. I'm not sure if that's helpful or not but here is another picture of the gorgeous Gentian flower from the Rock Garden at Kew Gardens. Of course my camera will have transformed the colour differently to the naked eye but this is close to what I saw a few weeks ago.
Gentian violet is perhaps the colour more commonly known by biologists. This is the name of a stain derived from coal tar that has a colour like some of the gentians. Gentian violet will highlight various details of cell structure in sections of plants or other organisms prepared for microscopic study. You might know it better as a treatment for fungal infections.
The flowers of Gentiana angustifolia look blue to me. Gentian flowers can be various colours even though we think of them typically as blue or violet: there are 360 species of Gentiana, although there used to be almost twice this number of species before genera such as Gentianella were chipped off. Gentiana angustifolia is presumably pollinated by insects such as butterflies, which visit the plant at all stages during their life cycle. They clearly have no trouble recognising blue, or violet.