L'Arc en Ciel, dated 1749, was executed during Vernet's Italian period, in which the artist's most expressive work was conceived. The majority of Claude-Joseph Vernet's oeuvre during the twenty years he lived in Italy explores mankind's precarious relationship with nature. Between 1734 and 1753, Vernet's marine compositions either celebrate the sea as a serene passage ripe with bountiful harvest; or demonstrate man's fragility in the face of nature's wrath, manifested in tumultuous swells and ominous skies. L'Arc en Ciel is unique within the spectrum of Vernet's expressive capacity as it manages to portray a balance between these two narratives. In the foreground fishermen haul in the day's catch on a rough and uneven coastline. This scene recedes into an expansive skyscape highlighted by the rainbow that arcs high into the clouds, seeming to chase the retreating storm out of the composition. L'Arc en Cielsurely must rank amongst one of the most romanticizing depictions of the Mediterranean coast in Vernet's body of work.

L'Arc en Ciel and its pendant, Seaport at Sunset, were both commissioned by Vernet's close friend and patron the Comte de Merles, Charles-Louis. Vernet's Livres de Raison does not record a sale for these two paintings in the year which the pictures are signed (1749), yet Vernet's diary reveals the close relationship between artist and patron. The Comte de Merles is described by Vernet's biographer, Leon Lagrange, as having met Vernet in Rome and the two spent time hunting together in October, November and December of 1749. The Comte later commissioned another pair of marine scenes (present location unknown, see L. Lagrange, op. cit., p. 350) from Vernet in 1772. .

The March 1784 sale of the Comte's impressive collection of paintings, furniture and works of art (in which L'Arc en Ciel was lot 22) was a notable event with three of the pictures being purchased for King Louis the XVI. L'Arc en Ciel and Seaport at Sunset  were probably separated soon after the sale of the Merles collection by Julliot and Paillet in Paris. Seaport at Sunset became part of the collection of Mr. Luke White of Luttrellstown, Ireland. It was then bought by the Guiness family, and passed from them to the Hon.Mrs. Plunkett. In 1976, Seaport at Sunset was exhibited in London (see P. Conisbee, catalogue of the exhibition, Claude Joseph Vernet 1714-1789, London, 1976). 

Claude-Joseph Vernet's career is truly representative of the spirit of the Grand Tour. He was born in Avignon and at the age of twenty, like most promising young artists of the 18th century, he traveled to Rome to study antiquity. In Rome, Vernet was granted access to L'Academie de France where he was encouraged to pursue ladnscape painting by the institution's director, Nicolas Vleughels. As a young artist, Vernet would have been exposed to the vedute of Claude Gellée, Salvator Rosa and Gaspard Dughet. He joined the workshop of Adrien Manglard, a successful French marine painter living in Rome. Like Manglard, Vernet;s established a burgeoning reputation as a masterful painter of marine scenes amongst European diplomats and nobility making the Grand Tour. While living in italy Vernet's often travelled from Rome to Naples, and although the port of L'Arc en Ciel is not identified by the artist, the topography visible is suggestive of the Neapolitan coast, and both the picture and its pendant are referred to as views of the port of Naples in the 1784 Merles sale catalogue. The late 1740s, during which L'Arc en Ciel was painted, is widely considered the  Vernet's most bold and creative and works from this stage in the artist's career are highly sought after. After twenty years in Italy, Vernet was summoned back to France in 1753 for the Royal commission of the Ports de France, where he would spend the remainder of his life.