Regarding the shade of blue, Yves Martin in his book on the Carabineers quotes correspondence from the Comte de Cessac, who was charged with delivering the new Carabineer uniform of 1810, with the Army Administration. He refers to the facing colour being "bleu celeste" (as opposed to bleu de ciel). This does appear to be rendered as a darker shade of blue then that widely represented, closer perhaps to bleu barbeau (which again seems to be darker than most traditional representations of cornflower blue). The main consideration seems to have been to use a shade of blue that was different to that worn by the Train of Artillery!
H0pe that this helps. Yves Martin's book is excellent, comprehensively illustrated and is well worth buying. It covers the history of the Carabineers from 1693 to 1871.
