Depression….

There is no “right” blue for the French. Or any other “right” uniform color before the invention of UV resistant cloth colors.

A unit that served a few weeks in Spanish summer got a very different shade of blue compared to the comrades that stayed in Depot in Paris had.

But even the northern sun was changing the Cloth shades.
British rifle green became more and more dark for that reason in 19th century. Just to counter the effect of UV bleaching.

Another problem was rain and cleaning. Washing a lot of color out of the cloth. British scarlet sometimes got pink.

You’re completely right, I’ve been waiting for somebody to say something like this. My father, who’s really into naval models, often has heard people asking about or selling “Nelson’s authentic Trafalgar yellow colour.” But of course no one thought to document the hex codes for the exact shade of the colour, and also every time it was repainted the shade changed, as it did after the ship had been out for a while. The colour would also be different on different parts of the ship, because they would get exposed to different things at different strengths. Also not to mention the fact that the Venetian red dye for British soldiers was chosen for its cheapness, nothing else, so they would continue going for the cheapest they could get until the red really became such a source of pride, and dyeing became a much more accurate science.

Enamel or acrylic ? 😉