This is to me an amusing perceptual phenomenon: the French tricolour comes in two varities: the navel ensign above, and the national flag below. The naval ensign was designed to be better distinguished by having unequal sized bands in a ratio. The French national flag's bands are equal:
|French National Flag|
National flag: 1:1:1.
Naval ensign: 30:33:37
Currently, the flag is 50 percent wider than its height (i.e. in the proportion 2:3) and, except in the French Navy, has stripes of equal width. Initially, the three stripes of the flag were not equally wide, being in the proportions 30 (blue), 33 (white) and 37 (red). Under Napoleon I, the proportions were changed to make the stripes' width equal, but by a regulation dated 17 May 1853, the navy went back to using the 30:33:37 proportions, which it continues to use.
Where the 30:33:37 ratio came from, I could not find any experimental basis for it. Perhaps they worked it out by trial-and-error. Or wild guessing.
The reason why they went back to the 30:33:37 ratio is because the flapping of the flag in the wind makes portions farther from the halyard seem smaller, and the red might not show well if there's little breeze.
I looked to determine whether other national flags also used disparate bands, and could not find other examples. For example, Ireland and Coté d'Ivorie uses green, white, and orange bands of the same size (1:1:1). Belgium used black, yellow and red bands in the 1:1:1 ratio. But then, do those countries have a navy? Italy has one; but its naval ensign has a crest in the middle of the white part.
|Flag of Ireland|
|Naval Flag of Italy|