From 1814 to 1830, the flag of the Kingdom of France was plain white.
The King is back in 1814, the white cockade spread and order of the provisional Government (April 13th) decided that the white ensign and the white cockade would be displayed on the war and merchant vessels. Nothing else was decided. So the white ensign became the white flag ashore until the return of Napoleon Ist in 1815 (these were the hundred days when the tricolour flag was flown from the imperial decree of March 9th), but during the return of Louis XVIII to Paris the white flag became legal again (July 7th).
In the aftermath of the July Revolution of 1830, King Louis-Philippe decided to restore the Tricolour flag. Since then, it has remained the national flag of France.
It was also the Naval Ensign of the Kingdom of France as used before 1789, and between 1814/15 and 1830.