Despite vast expanses of blue seas and skies, it’s always been an unusual colour in nature. Precious few fruits, animals or stones are blue, so the flashes of it we catch sight of – like a kingfisher in flight – seem magical, and the intensity of a rare blue sapphire can be hypnotic.

Robert Frost found this curious, given that the majesty of the sky offers so much of it, and expressed his feelings in the 1925 poem Fragmentary Blue:

Why make so much of fragmentary blue
In here and there a bird, or butterfly,
Or flower, or wearing-stone, or open eye,
When heaven presents in sheets the solid hue?

Because of its association with the celestial and the infinite, blue has been prized in art for centuries. Tutankhamun’s death mask from around 1323 BC combines gold with blue lapis lazuli and turquoise. Ceramicists of the Tang dynasty in seventh-century China innovated the use of blue pigments from cobalt ores, imported from Persia. Renaissance Italian artists expected to pay more for ultramarine pigments than for gold. And until a man-made pigment was invented in France in 1826, blue remained horribly expensive.

Ultramarine – named for having crossed oceans from far-off lands – was made using lapis lazuli, a semi-precious stone mined in Afghanistan, that was crushed and ground to create the luminous colour. “Ultramarine blue is a glorious, lovely and absolutely perfect pigment beyond all the pigments,” wrote the 15th-century artist Cennino.

Renaissance artists sometimes listed the cost of ultramarine separately on their bills to patrons. It was reserved for painting clear skies, or the Virgin and Christ child’s robes in altar pieces and holy scenes. Everyone knew its value, so plentiful use of blue in a painting reflected the wealth and status of the patron commissioning the work.

In his "Life of the Artists", gossipy Renaissance biographer Giorgio Vasari illustrates this with a story about Italian painter Pietro Perugino. His patron, a Florentine prior, provided plenty of ultramarine for a Nativity he had commissioned, but hovered in the studio all the time Perugino was working on the picture, muttering fretfully about the amount being used, and clearly suspicious that the artist might be cheating him.

Resenting this thinly disguised mistrust, Perugino pretended that he’d gradually used the entire stock, before presenting his patron with a dish of almost all the original pigment at the end of the day, saying, “Father, this is yours; learn to trust honest men, who never cheat those who trust them, although, if they wished, they could cheat such distrustful persons as yourself.”

Along with these artistic associations with holiness and the heavens, blue also has a long history as a symbol of nobility. Having blue blood – or “sangre azul” was a measure of high social status in medieval Spain, where pale skin and visible veins distinguished nobles from weatherbeaten outdoor workers.

For women in particular, a tracery of blue veins showing through the skin on hands, wrists and breasts was a mark of beauty. In his 1606 play "Antony and Cleopatra", Shakespeare has the Egyptian queen graciously condescending to offer her hand for a humble messenger to kiss – as long as he brings good news of Antony.

‘If thou so yield him, there is gold, and here
My bluest veins to kiss — a hand that kings
Have lipped, and trembled kissing.’
(Act 2 Sc 5)

Sadly, the poor man ends up being threatened with a knife rather than taking his reward, but Cleopatra’s boast about her blue-toned skin emphasises its importance. By the 19th century in the UK, “blue blooded” was understood by Victorians to mean being of noble birth.

Of course blue veins aren’t always delicate and tempting, as the late, great comedian Joan Rivers quipped: "I said to my husband, 'My boobs have gone, my stomach's gone, say something nice about my legs'. He said, ‘Blue goes with everything’."

There’s a darker side to the colour, too, captured by Victorian poet AE Houseman in his 1895 collection "A Shropshire Lad", describing the anguish of nostalgia for the lost days of the past:

Into my heart an air that kills
From yon far country blows:
What are those blue remembered hills,
What spires, what farms are those?

That is the land of lost content,
I see it shining plain,
The happy highways where I went
And cannot come again.

More cheerfully, his fellow Victorians sent each other coded messages through the popular “language of flowers”, useful in a society where plain speaking was not always possible, especially when wooing. Blue flowers had their own meaning. Hyacinths indicated, “Your loveliness charms me”. Canterbury Bells assured the recipient that, “Your letter received”. More troubling were cornflowers, which meant, “Be gentle with me”.

Finally, considering the earthy colours that dominate the natural world, author and art historian James Fox (speaking on historyextra.com’s podcast) points out that it came as a wondrous surprise to many when space travel in the 1960s allowed us high enough to look back at a beautiful “blue planet”; its hazy nimbus being created not just by the vast oceans but by the optical scatterings of blue wavelengths across the atmosphere.

It’s this unattainable, untouchable quality that gives blue its mystery and beauty, and why, while there’s a sky above us, it will always be earth’s favourite colour.