Ohoh!
My apologies, ADM, for choosing this worst picture.
I thought you meant the last picture because its the only one with some kind of light blue (but thats of course because of the flair overexposing all of that image.)
This is the best picture showing clear blue in stead of underexposed black:
And I still see very dark blue here while the white is real white so we should not blame the (yellow toned?) artificial lighting of that museum.
Apart from this: Are we talking about pre-1813 voltigeurs of the line or of the light infantry?
Of course, every exception is possible. As long as the color is not too chemically strong. There were even white uniforms between 1806 and 1809 because of the lack of indigo. But why focus on the exceptions?
ADM wrote:which can be even more light under the sun
I think you are forgetting sunlight (and washing and dirt) also destroys the color intensity. We had the same discussion last year about some green cavalry uniforms. Also then there was confusion about the difference between light (more white less color) and bright (strong light color)
Dark blue becomes pale grey-blue, not bright sky blue. Thats technically another color I think.
Dark green does not become apple green by weather but gets grey-green or minth-green.
I like to compare such blue uniform with a blue jeans: very dark blue when we buy it (and not bleached in the factory on forehand) , but due to washing and sunlight it becomes light pale blue and then it falls apart before it would become completely white. It never becomes sky blue halfway that process.