Eugene Buquoy was a French officer who studied and published uniform illustrations of the Consular and Napoleonic armies.
His wiki is in French, but can be translated online:
Born in 1879, he studied at St. Cyr. The son of an army doctor, he began collecting illustrations and information on uniforms by age 11.
He saw service in World War 1, and ended the war as a Captain, having received the Croix de Guerre and the Legion d’Honneur. He published his first books in 1935 and passed away in 1958.
His books are still available, and often command higher prices. However used books in decent shape can be found and I have a few of them. They are in French, but anyone with a passing acquaintance with high school French can glean the information. Of course the internet is a big help.
What makes the books so outstanding are the illustrations. Unusual uniforms and variations abound, all in full colour.
Here’s a quick survey of those I’ve managed to find:
Imperial Guard Cavalry
Infantry of the Imperial Guard
“Passepoil” or piping, referring to the uniforms of musicians and trumpeters.
Dragoons and Guides