The flag of France is based on three vertical stripes coloured blue, white, and red. It is widely known as the French Tricolour or simply, the Tricolour. The French flag is one of the most fascinating and iconic in European history.
The French Flag origin is inextricably linked to the French Revolution (1789- 1799), but the flag of France has changed over the centuries, depending on who ruled the country. The early coat of arms of the French kings in the early 1200s was a blue crest decorated with gold lily flowers (fleurs-de-lis), and the standard of the Bourbon family, who ruled France until the French Revolution from the late 16th century, was a white backdrop with gold fleurs-de-lis.
During the Revolution, blue and red rosettes were worn by the militia, in keeping with the colours of the French coat of arms as well as the red and blue flag of Paris. At the end of July 1789 when the new national police force, the National Guard, was formed, its commander, Marie Joseph Yves Gilbert du Motier, Marquis de Lafayette, created a rosette of blue, white and red as their emblem. This is thought to be one of the first times the Tricolore was used to represent France.
The Tricolore flag wasn’t displayed that much during the Revolution itself, but its revolutionary connotations were already etched into its short history. Aside from a short period (1814-1830) after the defeat of Napoleon in the Battle of Waterloo when the Bourbon monarchy returned to power and reinstated the white fleur-de-lis flag, it has remained France’s flag ever since.
Source:
https://theculturetrip.com/europe/france/articles/fascinating-history-behind-french-flag/