The Côte d'Azur (coast of azure) is a nickname given by France to the County of Nice after its annexation in 1860, because the climate was similar to that of the north of Italy, even in winter, with a sky as blue as its sea.

The Côte d'Azur (the French Riviera) gets its distinctive azure-blue color from a combination of geological and optical factors. The sea floor in this region is largely composed of limestone pebbles and white sand, which reflect sunlight back through the water with high clarity. When the sun’s rays hit the Mediterranean, the water molecules and suspended fine limestone particles scatter the shorter wavelengths of light—specifically the blues and violets—more effectively than the longer red wavelengths (a phenomenon known as the Tyndall effect). Additionally, the lack of large river estuaries flowing into this part of the coast means there is very little sediment or organic runoff to "cloud" the water with greens or browns. This results in a startlingly clear, deep-blue hue that prompted French writer Stéphen Liégeard to coin the name "Côte d'Azur" in 1888, a name that remains perfectly accurate for the vibrant coastal waters travelers see today in 2026.